@article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/106466, title ="The Lavic Lake Fault: A Long-Term Cumulative Slip Analysis via Combined Field Work and Thermal Infrared Hyperspectral Airborne Remote Sensing", author = "Witkosky, Rebecca A. and Stock, Joann M.", journal = "Remote Sensing", volume = "12", number = "21", pages = "Art. No. 3586", month = "November", year = "2020", doi = "10.3390/rs12213586", issn = "2072-4292", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201105-160425687", note = "© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). \n\nReceived: 6 October 2020 / Revised: 26 October 2020 / Accepted: 29 October 2020 / Published: 1 November 2020. \n\n(This article belongs to the Special Issue Hyperspectral and Multispectral Imaging in Geology). \n\nWe thank the Marine Corps Air Ground Combat Center in Twentynine Palms, California, for allowing access to the military base. We thank Ken Hudnut, Janet Harvey, Kate Scharer, and Sinan Akçiz for their help and support in fieldwork, performing this research, and preparing this manuscript. We also thank the Editors for handling this manuscript, and Nick Van Buer and two anonymous reviewers for helping improve the content. The new data presented in this study are available through Caltech’s Research Data Repository (https://doi.org/10.22002/d1.1182). The data used in this study from previously published geologic maps are available from the U.S. Geological Survey’s National Geologic Map Database (https://ngmdb.usgs.gov/ngmdb/ngmdb_home.html); the references also indicate the specific URLs for each item. \n\nThis research was funded by the National Science Foundation (NSF) Graduate Research Fellowship Program under Grant No. 1144469 awarded to R. Witkosky, and by Southern California Earthquake Center (SCEC) Award No. 14160 awarded to J. Stock. This paper is SCEC Contribution No. 8898. SCEC is funded by NSF Cooperative Agreements EAR-1033462 & EAR-0529922, and United States Geological Survey Cooperative Agreements G12AC20038 & 07HQAG0008. Mako airborne hyperspectral imagery was acquired under the auspices of the Aerospace Corporation’s Independent Research and Development program. \n\nAuthor Contributions. Conceptualization, R.A.W., J.M.S. and D.M.T.; methodology, R.A.W., J.M.S., D.M.T., K.N.B., D.K.L. and F.J.S.; software, R.A.W., J.M.S., K.N.B. and P.D.J.; validation, R.A.W., J.M.S, D.M.T., K.N.B., P.M.A., P.D.J.; formal analysis, R.A.W.; investigation, R.A.W., J.M.S., D.M.T, K.N.B., P.M.A., P.D.J., D.K.L., F.J.S.; resources, R.A.W., J.M.S., D.M.T., P.M.A.; data curation, R.A.W., J.M.S., D.M.T. and K.N.B.; writing—original draft preparation, R.A.W. and J.M.S.; writing—review and editing, R.A.W., J.M.S., D.M.T., K.N.B., P.M.A., P.D.J., D.K.L. and F.J.S.; visualization, R.A.W., P.D.J. and F.J.S.; funding acquisition, R.A.W, J.M.S. and D.M.T. All authors have read and agreed to the published version of the manuscript. \n\nThe authors declare no conflict of interest.", revision_no = "10", abstract = "The 1999 Hector Mine earthquake ruptured to the surface in eastern California, with >5 m peak right-lateral slip on the Lavic Lake fault. The cumulative offset and geologic slip rate of this fault are not well defined, which inhibits tectonic reconstructions and risk assessment of the Eastern California Shear Zone (ECSZ). With thermal infrared hyperspectral airborne imagery, field data, and auxiliary information from legacy geologic maps, we created lithologic maps of the area using supervised and unsupervised classifications of the remote sensing imagery. We optimized a data processing sequence for supervised classifications, resulting in lithologic maps over a test area with an overall accuracy of 71 ± 1% with respect to ground-truth geologic mapping. Using all of the data and maps, we identified offset bedrock features that yield piercing points along the main Lavic Lake fault and indicate a 1036 +27/−26 m net slip, with 1008 +14/−17 m horizontal and 241 +51/−47 m vertical components. For the contribution from distributed shear, modern off-fault deformation values from another study imply a larger horizontal slip component of 1276 +18/−22 m. Within the constraints, we estimate a geologic slip rate of <4 mm/yr, which does not increase the sum geologic Mojave ECSZ rate to current geodetic values. Our result supports previous suggestions that transient tectonic activity in this area may be responsible for the discrepancy between long-term geologic and present-day geodetic rates.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/105899, title ="Continental Interior and Edge Breakup at Convergent Margins Induced by Subduction Direction Reversal: A Numerical Modeling Study Applied to the South China Sea Margin", author = "Li, Fucheng and Sun, Zhen", journal = "Tectonics", volume = "39", number = "11", pages = "Art. No. e2020TC006409", month = "November", year = "2020", doi = "10.1029/2020tc006409", issn = "0278-7407", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201007-140342146", note = "© 2020 American Geophysical Union. \n\nIssue Online: 30 October 2020; Version of Record online: 30 October 2020; Accepted manuscript online: 06 October 2020; Manuscript accepted: 29 September 2020; Manuscript revised: 24 September 2020; Manuscript received: 02 July 2020. \n\nThis research was supported by the Guangdong NSF research team project (2017A030312002), the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (GML2019ZD0205), the K. C. Wong Education Foundation (GJTD‐2018‐13), the Strategic Priority Research Program of the Chinese Academy of Science (XDA13010303), the Chinese Academy of Sciences (Y4SL021001, QYZDY‐SSWDQC005, 133244KYSB20180029, and ISEE2019ZR01), the NSFC project (41606073, 41890813, and 41576070), the IODP‐China Foundation, the OMG Visiting Fellowship (OMG18‐15), and the Hong Kong Research Grant Council Grants (Nos. 14313816 and 14304820). We thank Fabio Crameri, Marta Pérez‐Gussinyé, two anonymous reviewers, editor Laurent Jolivet, and associated editor Laurent Husson for their constructive comments that contributed to improving the manuscript. An earlier review by Guillaume Duclaux is also appreciated. \n\nData Availability Statement: Data can be obtained from a repository (https://figshare.com/s/ed3174627a7090e9ad45).", revision_no = "26", abstract = "The dynamics of continental breakup at convergent margins has been described as the results of backarc opening caused by slab rollback or drag force induced by subduction direction reversal. Although the rollback hypothesis has been intensively studied, our understanding of the consequence of subduction direction reversal remains limited. Using thermo‐mechanical modeling based on constraints from the South China Sea (SCS) region, we investigate how subduction direction reversal controls the breakup of convergent margins. The numerical results show that two distinct breakup modes, namely, continental interior and edge breakup (“edge” refers to continent above the plate boundary interface), may develop depending on the “maturity” of the convergent margin and the age of the oceanic lithosphere. For a slab age of ~15 to ~45 Ma, increasing the duration of subduction promotes the continental interior breakup mode, where a large block of the continental material is separated from the overriding plate. In contrast, the continental edge breakup mode develops when the subduction is a short‐duration event, and in this mode, a wide zone of less continuous continental fragments and tearing of the subducted slab occur. These two modes are consistent with the interior (relic late Mesozoic arc) and edge (relic forearc) rifting characteristics in the western and eastern SCS margin, suggesting that variation in the northwest‐directed subduction duration of the Proto‐SCS might be a reason for the differential breakup locus along the strike of the SCS margin. Besides, a two‐segment trench associated with the northwest‐directed subduction is implied in the present‐day SCS region.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/106221, title ="Moho Depth of Northern Baja California, Mexico, From Teleseismic Receiver Functions", author = "Ramirez, E. E. and Bataille, Klaus", month = "September", year = "2020", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201022-104923841", note = "Published Online: Fri, 18 Sep 2020. \n\nPart of the financial support for this project was provided by CONACYT (CB-2009-133019 SEP-CONACYT). The first author worked under the Scholarship Number 254218 granted by the National Council of Science and Technology of Mexico (CONACYT), the CONACYT 2018 Foreign Mobility Fellowship (291250), and by the Mobility Fellowship granted by the Autonomous University of Baja California: research residence (announcement 76). Alejandra Núñez-Leal facilitated teleseismic data streams from the local seismic network (RESNOM). For the installation and service for the seismic stations, the authors acknowledge Oscar Gálvez, Luis Orozco, and Ignacio Méndez, from the Earth Sciences Division of CICESE. Sergio Arregui provided the main script used for creating the maps in Generic Mapping Tools. \n\nData and Resources: Raw and processed seismic signals, as well as the poles and zeros of stations and main scripts used can be found in https://zenodo.org/record/4017974#.X1Z_SHkzaUl (doi: 10.5281/zenodo.4017974). Teleseismic catalog was obtained from the USGS Earthquake Catalog, available at https://earthquake.usgs.gov/earthquakes/search/ (last accessed September 2020). Some computations were made writing Matlab scripts, available at https://www.mathworks.com/products/matlab.html (last accessed September 2020). Data from the Northwest Mexico Seismic Network are available, since 10 September 2014, from the Incorporated Research Institutions for Seismology Data Management Center (IRIS-DMC) at http://ds.iris.edu/mda/BC (last accessed September 2020). The teleseismic data used in this study and the stations Dataless are available upon request to M. Alejandra Nuñez-Leal. (anunez@cicese.mx). Preprocessing scripts (macros) were written in Seismic Analysis Code (SAC), available at http://ds.iris.edu/ds/nodes/dmc/software/downloads/sac/ (last September 2020). ObsPy is available at https://github.com/obspy/obspy/wiki (last accessed July 2019). Spyder is available at https://www.spyder-ide.org/ (last accessed September 2020). The rf Python framework for receiver function computations is available at https://rf.readthedocs.io/en/latest/ (last accessed July 2019). The P-wave travel times were computed, and added to earthquakes data with TauP, available at http://www.seis.sc.edu/TauP/ (last accessed September 2020). The FuncLab toolbox used for estimating the Moho depth is available at https://robporritt.wordpress.com/software/ (last accessed September 2020). Some plots were made using the Generic Mapping Tools v.5.3.1 available at http://gmt.soest.hawaii.edu/ (last accessed September 2020).", revision_no = "13", abstract = "We estimated Moho depth from data recorded by permanent and temporary broadband seismic stations deployed in northern Baja California, Mexico using the receiver function technique. This region is composed, mainly, of two subregions of contrasting geological and topographical characteristics: The Peninsular Ranges of Baja California (PRBC), a batholith with high elevations (up to 2600 m above mean sea level); and the Mexicali Valley (MV) region, a sedimentary environment at around the mean sea level. Crustal thickness derived from the P-to-S converted phases at 29 seismic stations were analyzed in 3 profiles: two that cross the two subregions, in a ~W-E direction, and the third one that runs over the PRBC in a N-S direction. For the PRBC region, Moho depths vary from 35 to 45 km, from 33°;N to 32°;N; and from 30 to 46 km depth from 32°;N to 30.5°;N. From a profile that crosses the subregions in the W-E direction; Moho depths vary from 45 to ~34 km under the PRBC; with an abrupt change of depth under the Main Gulf Escarpment, from ~32 to 30 km; and depths of 17-20 km under the MV region. Moho depths of the profile that runs, of an almost W-E direction at ~31.5°; N, follow the eltimetry from 0 to 2600 m: from ~30 to 40 km; and became shallower (16 km depth) as the profile reaches the Gulf of California. These results show that deeper Moho is related to higher elevations with an abrupt change under the Main Gulf Escarpment.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/106262, title ="Strike-slip Enables Subduction Initiation beneath a Failed Rift: New Seismic Constraints from Puysegur Margin, New Zealand", author = "Shuck, Brandon and Van Avendonk, Harm", month = "July", year = "2020", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201023-130721209", note = "Published Online: Thu, 23 Jul 2020. \n\nWe thank the captain, crew, and science party of the R/V Marcus Langseth for their efforts during the South Island Subduction Initiation Experiment. Thank you to Kelly Olsen, Andrew Gase, Justin Estep, and Dominik Kardell for guidance in seismic processing and invaluable feedback on seismic interpretations. Special thanks to the University of Texas Institute for Geophysics (UTIG) Marine Geology and Geophysics group for fruitful discussions which significantly improved this work. We are grateful to Mark Wiederspahn for his technical support and assistance with computational resources, and Marcy Davis and Dan Duncan for\nhelping with multibeam and backscatter data gridding and visualization. The authors wish to acknowledge and thank the Paradigm University Grant Program of Emerson E&P Software for the use of Paradigm Echos for data processing in this project. The authors also wish to thank the Halliburton/Landmark University Grant program for the use of Decision Space Desktop and GeoProbe software used in the interpretation of this data. We thank IHS-Markit for a university educational license for Kingdom software, provided to Caltech, for seismic data visualization and interpretation. Research in this manuscript was supported by the National Science Foundation through awards OCE-1654689 (UT Austin) and OCE-1654766 (Caltech). \n\nUninterpreted and interpreted seismic images shown in this study can be found in the supporting information. Underway geophysical data from MGL1803 are available from the Rolling Deck Repository (http://doi.org/10.7284/907966). Raw and processed seismic data used in this study are available through the Marine Geoscience Data System (http://doi.org/10.1594/IEDA/324659/). This is UTIG Contribution #XXXX.", revision_no = "8", abstract = "Subduction initiation often takes advantage of previously weakened lithosphere and may preferentially nucleate along pre-existing plate boundaries. To evaluate how past tectonic regimes and inherited lithospheric structure might lead to self-sustaining subduction, we present an analysis of the Puysegur Trench, a young subduction zone with a rapidly evolving tectonic history. The Puysegur margin, south of New Zealand, has experienced a transformation from rifting to seafloor spreading to strike-slip, and most recently to incipient subduction, all in the last ~45 million years. Here we present deep-penetrating multichannel reflection (MCS) and ocean-bottom seismometer (OBS) tomographic images to document crustal structures along the margin. Our images reveal that the overriding Pacific Plate beneath the Solander Basin contains stretched continental crust with magmatic intrusions, which formed from Eocene-Oligocene rifting between the Campbell and Challenger plateaus. Rifting was more advanced to the south, yet never proceeded to breakup and seafloor spreading in the Solander Basin as previously thought. Subsequent strike-slip deformation translated continental crust northward causing an oblique collisional zone, with trailing ~10 Myr old oceanic lithosphere. Incipient subduction transpired as oceanic lithosphere from the south forcibly underthrust the continent-collision zone. We suggest that subduction initiation at the Puysegur Trench was assisted by inherited buoyancy contrasts and structural weaknesses that were imprinted into the lithosphere during earlier phases of continental rifting and strike-slip along the plate boundary. The Puysegur margin demonstrates that forced nucleation along a strike-slip boundary is a viable subduction initiation scenario and should be considered throughout Earth's history.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/103318, title ="Stratigraphic architecture of Solander Basin records Southern Ocean currents and subduction initiation beneath southwest New Zealand", author = "Patel, Jiten and Sutherland, Rupert", journal = "Basin Research", month = "May", year = "2020", doi = "10.1111/bre.12473", issn = "0950-091X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200519-132017615", note = "© 2018 Wiley. \n\nAccepted manuscript online: 18 May 2020.", revision_no = "5", abstract = "Solander Basin is currently characterised by subduction initiation at the Pacific‐Australia plate boundary, where high biological productivity is found at the northern edge of the Antarctic Circumpolar Current. Sedimentary architecture results from tectonic influences on accommodation space, sediment supply, and ocean currents (via physiography); and climate influence on ocean currents and biological productivity. We present the first seismic‐stratigraphic analysis of Solander Basin based on high‐fold seismic‐reflection data (voyage MGL1803, SISIE). Solander Trough physiography formed by Eocene rifting, but basinal strata are mostly younger than ~17 Ma, when we infer Puysegur Ridge formed and sheltered Solander Basin from bottom currents, and mountain growth onshore increased sediment supply. Initial inversion on the Tauru Fault started at ~15 Ma, but reverse faulting from 12 to ~8 Ma on both the Tauru and Parara Faults was likely associated with reorganization and formation of the subduction thrust. The new seabed topography forced sediment pathways to become channelized at low points or antecedent gorges. Since 5 Ma, southern Puysegur Ridge and Fiordland mountains spread out towards the east and Solander Anticline grew in response to ongoing subduction and growth of a slab. Solander Basin had high sedimentation rates because: (1) it is sheltered from bottom currents by Puysegur Ridge; and (2) it has a mountainous land area that supplies sediment to its northern end. Sedimentary architecture is asymmetric due to the Subtropical Front, which moves pelagic and hemi‐pelagic sediment, including dilute parts of gravity flows, eastward and accretes contourites to the shelf south of Stewart Island. Levees, scours, drifts, and ridges of folded sediment characterize western Solander Basin, whereas hemi‐pelagic drape and secondary gravity flows are found east of the meandering axial Solander Channel. The high‐resolution record of climate and tectonics that Solander Basin contains may yield excellent sites for future scientific ocean drilling.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/101186, title ="Scales of Stress Heterogeneity Near Active Faults in the Santa Barbara Channel, Southern California", author = "Persaud, Patricia and Pritchard, Edward H.", journal = "Geochemistry, Geophysics, Geosystems", volume = "21", number = "1", pages = "Art. No. e2019GC008744", month = "January", year = "2020", doi = "10.1029/2019gc008744", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200210-081539156", note = "© 2020 American Geophysical Union. \n\nReceived 30 SEP 2019; Accepted 30 DEC 2019; Accepted article online 3 JAN 2020. \n\nWe thank three anonymous reviewers, the Editor, Thorsten Becker, and the Editor in Chief, Claudio Faccenna, for their insightful comments and suggestions, which significantly improved this manuscript. The raw dataset of digital well curves used in this study was provided by oil companies in the Southern California area and is proprietary and subject to confidentiality agreements. The well names are anonymized. The well locations, well paths and depths, and all other information derived during the processing are presented in the paper. Figures were prepared with the Generic Mapping Tool (GMT) software (Wessel et al., 2013) and Petrel. We thank C. Sorlien, M. Kamerling, C. Nicholson, and R. Behl for sharing their work and Sorlien for compiling the seismic profiles shown in Figures 2c and 3c. We thank the Geology and Geophysics Department at Louisiana State University for supporting this project. Portions of this research were conducted with high performance computing resources provided by Louisiana State University (http://www.hpc.lsu.edu). This research was partly supported by the Southern California Earthquake Center (Contribution No. 8267). SCEC is funded by NSF Cooperative Agreement EAR‐1033462 & USGS Cooperative Agreement G12 AC20038.", revision_no = "9", abstract = "The Santa Barbara Channel represents the offshore portion of the Ventura Basin in Southern California. Ongoing transpression related to a regional left step in the San Andreas Fault has led to the formation of E‐W trending en‐echelon fault systems that accommodate localized shortening across the basin. Recent studies have suggested that faults within the channel could be capable of a multisegment rupture and producing a M_w 7.7–8.1 tsunamigenic earthquake. However, dynamic rupture models producing these results do not account for stress heterogeneity. With only sparse information available on the stress field in this region, further borehole‐derived stress constraints are essential for obtaining a more comprehensive understanding of the hazards related to the complex fault systems. We used caliper logs from 19 wells obtained from industry to identify stress‐induced borehole breakouts beneath the Holly and Gail oil platforms in the channel. Our newly developed forward modeling technique provides constraints on the orientations and relative magnitudes of the three principal stresses. At Gail, we determine a reverse faulting stress regime (S_(Hmax) = 1.7; S_(hmin) = 1.6; SV = 1.0) and an S_(Hmax) azimuth of N45°E. Our results are consistent with local structures, which reflect deeper regional scale trends, and with similar studies onshore nearby. At Holly, an S_(Hmax) rotation from ~N36°W to ~N57°E occurs across ~100 m depth in a single well and differs from nearby results, indicating that short‐length scale (<10 km laterally and <1 km in depth) stress heterogeneity is associated with complex changes in fault geometry.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/98509, title ="Seismic characteristics and evolution of post-rift igneous complexes and hydrothermal vents in the Lingshui sag (Qiongdongnan basin), northwestern South China Sea", author = "Wang, Lijie and Sun, Zhen", journal = "Marine Geology", volume = "418", pages = "Art. No. 106043", month = "December", year = "2019", doi = "10.1016/j.margeo.2019.106043", issn = "0025-3227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190909-093502804", note = "© 2019 Published by Elsevier. \n\nReceived 28 October 2018, Revised 4 September 2019, Accepted 7 September 2019, Available online 9 September 2019.", revision_no = "9", abstract = "The study of morphology, distribution, and characteristics of igneous complexes has great significance to the understanding of magma plumbing processes, geodynamics, and tectonic evolution of continental margins. Previous studies concentrated partly on the magma-rich rifted basins, where the lateral magma transport mainly affects the igneous complexes' connection and distribution. However, due to seismic wave shielding effects of the large shallow magmatic bodies, the underlying igneous complexes and their corresponding magma plumbing systems in the magma-poor rifted margins are still in debate. In this study, 2D/3D seismic data and well data are utilized to describe the morphology, architecture, and spatial-temporal distribution of igneous complexes in the Lingshui sag of the Qiongdongnan basin, northwestern South China Sea margin. The identified igneous complexes include 98 intrusive sills and feeder dykes beneath some of the isolated sills. Twenty-six cone-shaped mounds that overlie intruded sills through internal disturbed conduits were also described. Drilled well samples and seismic expressions suggest that these mounds are hydrothermal vents. A uniform Bottom Mounds Horizon of these vents suggests that they probably formed at the same time. Constrained by biostratigraphic data and sedimentation rate of underlying and overlying sedimentary layers, the magma emplacement was dated to the middle Miocene (ca. 14.6\u202fMa). Most of the hydrothermal vents are distributed along the F2 fault zone and have direct linkage with the underlying sills, while the large sill complexes that are connected with limited vents are mainly present above the hyperextended continental crust, where the crust thins to 6–10\u202fkm. The sills intruded into different layers, from the lower Oligocene to the lower Miocene and the emplaced depth of sills is 1.2–6.3\u202fkm, whether or not they feed any vents above. Unlike most of the large volume and laterally linked sills found in the magma-rich rifted margins, the scattered distribution of sills at different levels indicates that dykes probably play an important role in magma transport, which might coexist with numerous polygonal or small faults and interference reflections. This work highlights the critical role of basin structures in controlling the distribution of post-rift igneous complexes in magma-poor margins, including thinned continental crust, sedimentary thickness, and faults.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/99329, title ="Microstructures documenting Cenozoic extension processes in the northern continental margin of the South China Sea", author = "Sun, Liheng and Sun, Zhen", journal = "International Geology Review", volume = "62", number = "7-8", pages = "1094-1107", month = "September", year = "2019", doi = "10.1080/00206814.2019.1669079", issn = "0020-6814", url = "https://resolver.caltech.edu/CaltechAUTHORS:20191017-132811087", note = "© 2019 Taylor & Francis. \n\nReceived 04 Mar 2019, Accepted 14 Sep 2019, Published online: 29 Sep 2019. \n\nThis work was supported by the Natural Science Foundation of Guangdong Province [2017A030312002]; K.C. Wong Education Foundation [GJTD-2018-13]; IODP-China and South China Sea Deep Project [91628301]. CAS P.I.F.I. visiting professor project [2019VMA0002]; National Natural Science Foundation of China [41576070, 41625007]; . This project used samples or data from the JOIDES Resolution Science Operator of the International Ocean Discovery Program, a large facility funded by the US National Science Foundation. \n\nThis research was supported by the research team project of Guangdong Natural Science Foundation (2017A030312002), K.C.Wong Education Foundation (GJTD-2018-13), South China Sea Deep Project (91628301), Guangdong Special Support Program to Y. D. J., CAS P.I.F.I. visiting professor project to J. M. S. (2019VMA0002) and the IODP-China Foundation. \n\nNo potential conflict of interest was reported by the authors.", revision_no = "14", abstract = "In order to investigate the thinning process of the northern continental margin of the South China Sea, petrographic and microstructural analysis were carried out on 20 greenschistfacies mylonite samples, which were obtained from Site U1504 of IODP Expedition 367/368 in the Outer Margin High of the region. The mineral assemblage of the greenschist-facies mylonite is chlorite + epidotite + albite (Ab = 94.7–99.9) + quartz, which contains 10-30% gravel components. Microstructural analysis indicates that the greenschist-facies mylonite experienced two episodes of deformation：early ductile deformation followed by a later stage of brittle deformatio. Both episodes of deformation suggest an extensional environment. The extensive development of bulging recrystallization (BLG) of quartz, microscopic fractures and fine granulation of albite suggest that the temperature of ductile deformation is about 300-400°C, compatiable with a ductile shearing at shallow crust levels (~5-10 km). Petrographic features suggest that the greenschist-facies mylonite might originate from volcanic sedimentary rocks or sedimentary rocks affected by the intrusion of mafic magma. Combined with seismic interpretation, we propose that the greenschist-facies mylonite might be formed by crustal exhumation after thick Mesozoic sediments were denuded by a major extension.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/96362, title ="Incipient subduction at the contact with stretched continental crust: The Puysegur Trench", author = "Gurnis, Michael and Van Avendonk, Harm", journal = "Earth and Planetary Science Letters", volume = "520", pages = "212-219", month = "August", year = "2019", doi = "10.1016/j.epsl.2019.05.044", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190613-105022288", note = "© 2019 Elsevier B.V. \n\nReceived 30 January 2019, Revised 16 April 2019, Accepted 28 May 2019, Available online 13 June 2019. \n\nSupported by the National Science Foundation through awards OCE-1654766 (to Caltech) and OCE-1654689 (to UT Austin). We thank the Captain and crew of the R/V Marcus G. Langseth and S. Saustrup, M. Davis and D. Duncan from UTIG for their exceptional effort during the expedition. We thank T. Gerya for a helpful review of an earlier version of our manuscript. All seismic data will be made available at the Academic Seismic Portal (ASP) at UTIG while all remaining data will be available at the Rolling Deck to Repository (R2R). This is UTIG Contribution #3455.", revision_no = "13", abstract = "A seismic Benioff zone and plate kinematics show Puysegur Trench south of New Zealand transitioning to subduction. Because the local structure and its influence on subduction initiation is poorly understood, we conducted a seismic survey with ocean bottom seismometers and multichannel seismic profiles. Our early results show that the overriding Pacific Plate beneath the Solander Basin is composed of block-faulted and thinned continental crust, and the inner trench wall of northern Puysegur Ridge is composed of folded and faulted sediment. The megathrust interface has been imaged and shows ∼500 m of downgoing, undisturbed sediments. Combining plate kinematic history with seismic velocity-inferred density, we show that the density difference across the plate boundary changed as oblique strike-slip plate motion juxtaposed dense oceanic crust with thinned continental crust. The density difference rapidly increased 18 to 15 Ma, coincident with subduction initiation, suggesting that compositional differences have a large influence on subduction initiation.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/93770, title ="A Crustal Velocity Model for the Peninsular Ranges of Baja California and Southwestern Laguna Salada, Mexico", author = "Ramírez Ramos, Erik Esteban and Vidal-Villegas, José Antonio", journal = "Seismological Research Letters", volume = "90", number = "3", pages = "1219-1229", month = "May", year = "2019", doi = "10.1785/0220180248", issn = "0895-0695", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190313-105427114", note = "© 2019 Seismological Society of America. \n\nPublished Online 13 March 2019. \n\nData and Resources: The map was made using the Generic Mapping Tools v.5.3.1, available at http://gmt.soest.hawaii.edu/ (last accessed August 2018). Some plots were made using the RAYINVR software available at http://terra.rice.edu/department/faculty/zelt/rayinvr.html (last accessed August 2018). Data from the Northwest Mexico Seismic Network (RESNOM) have been available, since 10 September 2014, from the Incorporated Research Institutions for Seismology Data Management Center (IRIS‐DMC) at http://ds.iris.edu/mda/BC (last accessed November 2018). The data used in this study are available upon request to María Alejandra Nuñez‐Leal (anunez@cicese.mx). MATLAB is available at https://www.mathworks.com/products/matlab.html (last accessed February 2019). \n\nThe first author worked with the support of the National Council of Science and Technology of Mexico (CONACYT) under the Scholarship Number 254218. The CONACYT provided financial support for this project (CB‐2009‐133019 SEP‐CONACYT). Financial support and facilities were also provided by The Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), via the Earth Sciences Division and the Department of Seismology; Autonomous University of Baja California, Mexico (UABC), and its Engineering Institute, and by CICESE by way of the Earth Science Division and the Department of Seismology. The publishing charges were funded by the Programa para el Desarrollo Profesional Docente (PRODEP) 2019 program at the Universidad Autónoma de Baja California, Instituto de Ingeniería. José Acosta Chang provided the temporary short‐period seismic stations for the project; Gustavo Arellano and Euclides Ruiz provided technical support and helped during the installation of the temporary stations. For the installation of instrumentation along the profiles, the authors acknowledge Rogelio Arce, Ignacio Méndez, Oscar Gálvez, Luis Orozco, Rogelio Reyes, German Martínez, Miguel Oliver, Leandro John, and Martín Pacheco, from the Earth Sciences Division of CICESE; Frida Cital, Agustín Oropeza, Erick Jonathan Ramírez, and Iván Ramírez, from the Engineering Institute of the UABC; and Jovanny Morán, from the Technical Institute of Ensenada (ITE), Baja California, Mexico. Sergio Arregui provided the main script used for generating maps in Generic Mapping Tools, and he also wrote the programs to download seismic time series from the Northwest Mexico Seismic Network (RESNOM) database. Rafael Barajas‐Angulo provided off‐road vehicles for the installation of the temporary stations in the Mexicali Valley (MV) region. Victor Dukes allowed us to perform the Laguna Salada (LS)‐blast on his property. The authors acknowledge the explosives company (Rivada), especially Glenda Vazquez and Engineer Dagguer, for their support and help during the blast in LS. The Ministry of Environmental and Natural Resources (SEMARNAT), the Mexican Secretariat of National Defense (SEDENA), the Government of the State of Baja California, and the Municipality of Mexicali, Baja California, granted the permits required to perform the blast in LS, Baja California.", revision_no = "18", abstract = "To see any change in seismic velocities that may be associated with an abrupt change in the regional geology (granitic rock in contact with sediments), we conducted a refraction seismic study in the Peninsular Ranges of Baja California, which is in the Mexico–southwestern Laguna Salada (LS) region. We installed 30 three‐component portable seismic stations, supplemented with two permanent six‐component stations of the Northwest Mexico Seismic Network (RESNOM). The stations, spaced ∼6\u2009\u2009km along a refraction profile, recorded two blasts; these were the direct shot located to the south of the city of Ensenada and the reverse shot in the southwestern LS (southwest–northeast direction). Record sections show seismograms with impulsive P arrivals at nearby stations. Rays from the two blasts were modeled (using asymptotic ray theory) to obtain a P‐wave velocity model from 0 to ∼15\u2009\u2009km depth along the refraction profile. Our modeling results are as follows: in the southwestern part of the profile (0–25 km distance), a low‐velocity zone of ∼2\u2009\u2009km/s exists between the depths of 0 and 3.5 km; in Sierra Juárez, the mean P‐wave velocity is ∼5.6\u2009\u2009km/s between the depths of 0 and 5 km; and in southwestern LS, a low‐velocity layer of ∼2.5\u2009\u2009km/s exists between the depths of 0 and ∼3\u2009\u2009km. We also modeled a layer of ∼6.5\u2009\u2009km/s between 4 and 12 km in the Ensenada–Ojos Negros region, and between the depths of 4 and 8 km below the southwestern LS. From a profile distance of 0 to 50 km, a velocity zone of ∼6.7\u2009\u2009km/s appears between the depths of 12 and 15 km.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94677, title ="Three-Dimensional Basin and Fault Structure From a Detailed Seismic Velocity Model of Coachella Valley, Southern California", author = "Ajala, Rasheed and Persaud, Patricia", journal = "Journal of Geophysical Research. Solid Earth", volume = "124", number = "5", pages = "4728-4750", month = "May", year = "2019", doi = "10.1029/2018JB016260", issn = "2169-9313", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190412-073116409", note = "© 2019 American Geophysical Union. \n\nReceived 21 JUN 2018; Accepted 6 APR 2019; Accepted article online 11 APR 2019. \n\nWe thank three anonymous reviewers, the Editor in Chief, Uri ten Brink, and the Associate Editor, Kelly Liu, for their comments and suggestions, which significantly improved this manuscript. The SSIP was funded by the U.S. Geological Survey Multihazards Demonstration Project, and the National Science Foundation Earthscope and Margins Programs through grants OCE‐0742253 (to California Institute of Technology) and OCE‐0742263 (to Virginia Tech). This research was supported by Southern California Earthquake Center (SCEC) awards 15190 and 18074 and the U.S. Geological Survey grant G15AP00062. SCEC is funded by NSF Cooperative Agreement EAR‐1033462 and USGS Cooperative Agreement G12AC20038. The SCEC contribution number for this paper is 8269. R. A. was also financially supported by the Society of Exploration Geophysicists Foundation through the merit‐based scholarship program. We refer to the extensive acknowledgments in Rose et al. (2013) for permissions and assistance received for SSIP as a whole. The data have been archived at the IRIS DMC (ds.iris.edu/pic‐ph5/metadata/SSIP/form.php). The 3‐D velocity model as well as the derived basement and estimated Z_(2.5) surfaces important for seismic hazard assessment is available for download at our LSU research webpage (https://www.geol.lsu.edu/persaud/Data.html). All figures are plotted using the Generic Mapping Tools (Wessel et al., 2013).", revision_no = "26", abstract = "The Coachella Valley in the northern Salton Trough is known to produce destructive earthquakes, making it a high seismic hazard area. Knowledge of the seismic velocity structure and geometry of the sedimentary basins and fault zones is required to improve earthquake hazard estimates in this region. We simultaneously inverted first P wave travel times from the Southern California Seismic Network (39,998 local earthquakes) and explosions (251 land/sea shots) from the 2011 Salton Seismic Imaging Project to obtain a 3‐D seismic velocity model. Earthquakes with focal depths ≤10 km were selected to focus on the upper crustal structure. Strong lateral velocity contrasts in the top ~3 km correlate well with the surface geology, including the low‐velocity (<5 km/s) sedimentary basin and the high‐velocity crystalline basement rocks outside the valley. Sediment thickness is ~4 km in the southeastern valley near the Salton Sea and decreases to <2 km at the northwestern end of the valley. Eastward thickening of sediments toward the San Andreas fault within the valley defines Coachella Valley basin asymmetry. In the Peninsular Ranges, zones of relatively high seismic velocities (~6.4 km/s) between 2‐ and 4‐km depth may be related to Late Cretaceous mylonite rocks or older inherited basement structures. Other high‐velocity domains exist in the model down to 9‐km depth and help define crustal heterogeneity. We identify a potential fault zone in Lost Horse Valley unassociated with mapped faults in Southern California from the combined interpretation of surface geology, seismicity, and lateral velocity changes in the model.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87386, title ="Rapid transition from continental breakup to igneous oceanic crust in the South China Sea", author = "Larsen, H. C. and Stock, J.", journal = "Nature Geoscience", volume = "11", number = "10", pages = "782-789", month = "October", year = "2018", doi = "10.1038/s41561-018-0198-1", issn = "1752-0894", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180627-101506778", note = "© 2018 Springer Nature Limited. \n\nReceived 11 November 2017; Accepted 04 July 2018; Published\n20 August 2018. \n\nThe authors acknowledge the Chinese National Offshore Oil and Gas Company (CNOOC) for providing access for Z.S. and H.C.L. to work on their large regional database of seismic reflection data, which CNOOC subsequently amended with acquisition of new data to document our selected drill sites. The authors thank the RV JOIDES Resolution crew and the IODP technical staff. The IODP–China office supported international workshops to develop the original drilling proposal. Co-principal investigators of the drilling proposal, P. Wang and C.-F. Li, are acknowledged for their contributions to planning. This research used data and samples provided by the International Ocean Discovery Program. A.K. and C.A.-Z. acknowledge support from NSF award no. OCE-1326927. D.Z. was supported by the Korean IODP program (KIODP). \n\nAuthor Contributions: H.C.L. was co-principal investigator (co-PI) for the original drilling proposal and interpretation of seismic data, co-chief scientist of expeditions 367/368, and directed the writing of the paper. G.M. is principal co-author, developed the geodynamic model jointly with H.C.L. and M.N. and was a shipboard scientist (structural geology) at expedition 368. M.N. was a shipboard scientist (structure/sedimentology) at expedition 367, carried out structural interpretation of syn-rift sedimentation, and contributed to model development and graphics. Z.S was co-PI for the original drilling proposal, interpretation of seismic data, and was co-chief scientist of expeditions 367/368. J.S. was co-chief scientist of expeditions 367/368 and co-proponent of the original drilling proposal. Z.J. was co-chief scientist of expeditions 367/368 and coordinated biostratigraphic interpretations. A.K. was expeditions 367/368 project manager. C.A.A.-Z. was expeditions 367/368 project manager and performed biostratigraphy. J.B., A.B., Y.C., M.D., A.F., J.H., T.W.H., K.H., B.H., X.H., B.J., C.Lei., L.L., Z.L., A.L., C.Lupi, A.McC., M.N., C.R., I.S., C.S., X.S., R.X., R.Y., L.Y., C.Z., J.Z., Y.Z., N.Z. and L.Z. collected the drilling data during IODP expedition 367 and participated in the writing of the paper. S.B., D.C., K.D., W.D., E.F., F.F., A.G., E.H., S.J., H.J., R.K., B.L., Y.L., J.L. (co-PI)., Chang Liu, Chuanlian Liu, L.N., N.O., D.W.P., P.P., N.Q., S.Sa., J.C.S., S.St., L.T., F.M.vdZ., S.W., H.W., P.S.Y. and G.Z. collected the drilling data during IODP expedition 368 and participated in writing of the paper. Roles on board are detailed in https://iodp.tamu.edu/scienceops/precruise/southchinasea2/participants.html. \n\nThe authors declare no competing interests. \n\nData availability: The data that support the findings of this study are available from the IODP Proceedings of Expeditions 367/368 (http://iodp.tamu.edu/publications/bibliographic_information/367368cit.html) to be published 28 September 2018. All IODP data from any expeditions can be obtained from https://doi.org/10.14379/iodp.proc.367368.2018. Further questions can be directed to the corresponding authors.", revision_no = "36", abstract = "Continental breakup represents the successful process of rifting and thinning of the continental lithosphere, leading to plate rupture and initiation of oceanic crust formation. Magmatism during breakup seems to follow a path of either excessive, transient magmatism (magma-rich margins) or of igneous starvation (magma-poor margins). The latter type is characterized by extreme continental lithospheric extension and mantle exhumation prior to igneous oceanic crust formation. Discovery of magma-poor margins has raised fundamental questions about the onset of ocean-floor type magmatism, and has guided interpretation of seismic data across many rifted margins, including the highly extended northern South China Sea margin. Here we report International Ocean Discovery Program drilling data from the northern South China Sea margin, testing the magma-poor margin model outside the North Atlantic. Contrary to expectations, results show initiation of Mid-Ocean Ridge basalt type magmatism during breakup, with a narrow and rapid transition into igneous oceanic crust. Coring and seismic data suggest that fast lithospheric extension without mantle exhumation generated a margin structure between the two endmembers. Asthenospheric upwelling yielding Mid-Ocean Ridge basalt-type magmatism from normal-temperature mantle during final breakup is interpreted to reflect rapid rifting within thin pre-rift lithosphere.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/83973, title ="Source Functions and Path Effects from Earthquakes in the Farallon Transform Fault Region, Gulf of California, Mexico that Occurred on October 2013", author = "Castro, Raúl R. and Stock, Joann M.", volume = "1", pages = "45-62", month = "December", year = "2017", issn = "2504-3625", isbn = "978-3-319-71564-3", url = "https://resolver.caltech.edu/CaltechAUTHORS:20171220-093808988", note = "© 2018 Springer International Publishing AG. \n\nFirst Online: 21 December 2017. \n\nReprinted from: Pure Appl. Geophys. 174 (2017), 2239–2256, 2016 Springer International Publishing. DOI 10.1007/s00024-016-1346-4. \n\nThe operation of the RESBAN network has been possible thanks to the financial support of the Mexican National Council for Science and Technology (CONACYT) (projects CB-2011-01-165401(C0C059), G33102-T and 59216). This paper was prepared while the first author (RRC) was on sabbatical year in Caltech. We thank Prof. Gurnis for the support provided. Dr. Lenin Avila-Barrientos facilitated part of the spectral records used to calculate the site functions. Antonio Mendoza Camberos pre-process the data from the RESBAN network and Arturo Perez Vertti maintains and operates the stations. We thank Dr. Edwards and the anonymous reviewer for their careful revisions, comments and suggestions which help us to improve the manuscript. We also acknowledge the Editor, Dr. Thomas H.W. Goebel.", revision_no = "15", abstract = "We determined source spectral functions, Q and site effects using regional records of body waves from the October 19, 2013 (M_w = 6.6) earthquake and eight aftershocks located 90 km east of Loreto, Baja California Sur, Mexico. We also analyzed records from a foreshock with magnitude 3.3 that occurred 47 days before the mainshock. The epicenters of this sequence are located in the south-central region of the Gulf of California (GoC) near and on the Farallon transform fault. This is one of the most active regions of the GoC, where most of the large earthquakes have strike–slip mechanisms. Based on the distribution of the aftershocks, the rupture propagated northwest with a rupture length of approximately 27 km. We calculated 3-component P- and S-wave spectra from ten events recorded by eleven stations of the Broadband Seismological Network of the GoC (RESBAN). These stations are located around the GoC and provide good azimuthal coverage (the average station gap is 39◦). The spectral records were corrected for site effects, which were estimated calculating average spectral ratios between horizontal and vertical components (HVSR method). The site-corrected spectra were then inverted to determine the source functions and to estimate the attenuation quality factor Q. The values of Q resulting from the spectral inversion can be approximated by the relations Q_P = 48.1 1±1^(f0:880:04) and QS = 135:4 1:1f ±^(0:580:03) and are consistent with previous estimates reported by Vidales-Basurto et al. (Bull Seism Soc Am 104:2027–2042, 2014) for the south-central GoC. The stress drop estimates, obtained using the ω^2 model, are below 1.7 MPa, with the highest stress drops determined for the mainshock and the aftershocks located in the ridge zone. We used the values of Q obtained to recalculate source and site effects with a different spectral inversion scheme. We found that sites with low S-wave amplification also tend to have low P-wave amplification, except for stations BAHB, GUYB and SFQB, located on igneous rocks, where the P-wave site amplification is higher.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/74473, title ="Active tectonics in the Gulf of California and seismicity (M > 3.0) for the period 2002–2014", author = "Castro, R. R. and Stock, J. M.", journal = "Tectonophysics", volume = "719-720", pages = "4-16", month = "November", year = "2017", doi = "10.1016/j.tecto.2017.02.015", issn = "0040-1951", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170222-145907573", note = "© 2017 Elsevier B.V. \n\nReceived 29 July 2016, Revised 14 February 2017, Accepted 20 February 2017, Available online 22 February 2017. \n\nThis paper was prepared while the first author (RRC) was on sabbatical year in Caltech. We thank CONACYT and Prof. Michael Gurnis for the support provided. The operation of the RESBAN network has been possible thanks to the financial support of the National Council of Science and Technology, Mexico (CONACYT) (projects CB-2011-01-165401(C0C059), G33102-T and 59216). Antonio Mendoza Camberos pre-process the data from the RESBAN network and Arturo Perez Vertti maintains and operates the stations. The authors thank the editors and the comments and suggestions of two anonymous reviewers.", revision_no = "18", abstract = "We present a catalog of accurate epicenter coordinates of earthquakes located in the Gulf of California (GoC) in the period 2002–2014 that permits us to analyze the seismotectonics and to estimate the depth of the seismogenic zone of this region. For the period April 2002 to December 2014 we use body-wave arrival times from regional stations of the Broadband Seismological Network of the GoC (RESBAN) operated by CICESE to improve hypocenter locations reported by global catalogs. For the northern region of the GoC (30°N–32°N) we added relocated events from the 2011-Hauksson-Yang-Shearer, Waveform Relocated Earthquake Catalog for Southern California (Hauksson et al., 2012; Lin et al., 2007). From October 2005 to October 2006 we incorporated hypcenters located by Sumy et al. (2013) in the southern GoC combining an array of ocean-bottom seismographs, of the SCOOBA experiment, with onshore stations of the NARS-Baja array. This well constrained catalog of seismicity highlights zones of active tectonics and seismic deformation within the North America-Pacific plate boundary. We estimate that the minimum magnitude of completeness of this catalog is Mc = 3.3 ± 0.1 and the b = 0.92 ± 0.04 value of the Gutenberg-Richter relation. We find that most earthquakes in the southern GoC are generated by transform faults and this region is more active than the central GoC region. However, the northern region, where most deformation is generated by oblique faults is as active as the southern region. We used the ISC catalog to evaluate the size distribution of seismicity of these regions, and the b value of the Gutenberg-Richter relation and found that b is slightly lower in the central GoC (b = 0.86 ± 0.02) compared to the northern (b = 1.14 ± 0.04) and the southern (b = 1.11 ± 0.04) regions. We observed seismicity that occurs in the Stable Central Peninsular Province, despite the fact that significant active deformation has not been identified in this region.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/78745, title ="Subsurface Geometry of the San Andreas Fault in Southern California: Results from the Salton Seismic Imaging Project (SSIP) and Strong Ground Motion Expectations", author = "Fuis, Gary S. and Bauer, Klaus", journal = "Bulletin of the Seismological Society of America", volume = "107", number = "4", pages = "1642-1662", month = "August", year = "2017", doi = "10.1785/0120160309", issn = "0037-1106", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170705-073528849", note = "© 2017 Seismological Society of America. \n\nManuscript received 10 October 2016. First Published on July 04, 2017. \n\nWe thank land owners for their cooperation in data collection for this study, without which the Salton Seismic Imaging Project (SSIP) could not have been completed: line 4, Torres Martinez tribe, U.S. Bureau of Land Management (Palm Springs office); line 6, Palm Springs tram, U.C. Irvine, Coachella Valley Association of Governments, and City of Yucca Valley. Please refer to the extensive acknowledgments in Rose et al. (2013) for permissions and assistance we received for SSIP as a whole. We thank R. J. Blakely, W. D. Mooney, K. Knudsen, and two anonymous reviewers for helpful reviews, and numerous colleagues for discussions. SSIP was supported by National Science Foundation (NSF) Grants 0742263, 9742253, and 0927446 and funds from the U.S. Geological Survey (USGS) and Southern California Earthquake Center (SCEC).", revision_no = "17", abstract = "The San Andreas fault (SAF) is one of the most studied strike‐slip faults in the world; yet its subsurface geometry is still uncertain in most locations. The Salton Seismic Imaging Project (SSIP) was undertaken to image the structure surrounding the SAF and also its subsurface geometry. We present SSIP studies at two locations in the Coachella Valley of the northern Salton trough. On our line 4, a fault‐crossing profile just north of the Salton Sea, sedimentary basin depth reaches 4 km southwest of the SAF. On our line 6, a fault‐crossing profile at the north end of the Coachella Valley, sedimentary basin depth is ∼2–3\u2009\u2009km and centered on the central, most active trace of the SAF. Subsurface geometry of the SAF and nearby faults along these two lines is determined using a new method of seismic‐reflection imaging, combined with potential‐field studies and earthquakes. Below a 6–9 km depth range, the SAF dips ∼50°–60° NE, and above this depth range it dips more steeply. Nearby faults are also imaged in the upper 10 km, many of which dip steeply and project to mapped surface fault traces. These secondary faults may join the SAF at depths below about 10 km to form a flower‐like structure. In Appendix D, we show that rupture on a northeast‐dipping SAF, using a single plane that approximates the two dips seen in our study, produces shaking that differs from shaking calculated for the Great California ShakeOut, for which the southern SAF was modeled as vertical in most places: shorter‐period (T<1\u2009\u2009s) shaking is increased locally by up to a factor of 2 on the hanging wall and is decreased locally by up to a factor of 2 on the footwall, compared to shaking calculated for a vertical fault.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/79231, title ="Observations of remotely triggered seismicity in Salton Sea and Coso geothermal regions, Southern California, USA, after big (M_W>7.8) teleseismic earthquakes", author = "Castro, Raúl R. and Clayton, Robert", journal = "Geofisica Internacional", volume = "56", number = "3", pages = "269-286", month = "July", year = "2017", issn = "0016-7169", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170720-074723751", note = "© 2017 Instituto de Geofísica is licensed under a Creative Commons Reconocimiento-NoComercial-SinObraDerivada 3.0 Unported License. \n\nReceived: September 27, 2016; accepted: January 08, 2017; published on line: July 01, 2017. \n\nThis paper was prepared while the first author (RRC) was on sabbatical year in Caltech. We thank CONACYT and Prof. Gurnis for the support provided. Antonio Mendoza helped us to prepare some maps. We used parametric data from the Caltech/USGS Southern California Seismic Network (SCSN); DOI: 10.7914/SN/CI; stored at the Southern California Earthquake Center. doi:10.7909/C3WD3xH1. We thank the two anonymous reviewers and the Editor Dr. Xyoli Pérez-Campos for their comments and suggestions.", revision_no = "10", abstract = "A relocated catalog was used to search for changes in seismicity rate in the Salton Sea and the Coso geothermal regions, southern California, USA, during and after large (M_W>7.8) teleseismic earthquakes. Seismicity in these two regions was analyzed within 30- day windows before and after the occurrence of five major earthquakes: the 2002 Denali fault, Alaska (M_W 7.9); the 2004 Sumatra-Andaman (M_W 9.2); the 2010 Central Chile (M_W 8.8); the 2011 Tohoku-Oki, Japan (M_W 9.1); and the 2012 Offshore Northern Sumatra (M_W 8.6) earthquakes. \n\nThe Denali (M_W 7.9) earthquake coincided with an increase in seismicity in the Salton Sea region the day when this remote event occurred, indicating that instantaneous triggered seismicity was likely related with the passage of its surface waves. However, in the Coso region the seismicity rate remained approximately constant during the 30-day observation period. The seismicity after the 2004 Sumatra-Andaman (M_W 9.2) earthquake increased in both regions 9 days after the mega-earthquake. The seismicity after the 2010 Chile (M_W 8.8) earthquake increased in both regions approximately 14 days after the remote event. The seismicity in Salton Sea and Coso regions increased 17 and 14 days, respectively, after the 2011 Japan (M_W 9.1) earthquake, suggesting that delayed triggered seismicity was induced after the passage of the surface waves in both regions. Similarly, 6 and 16 days after the 2012 northern Sumatra (M_W 8.6) earthquake the seismicity also increased in Salton Sea and Coso regions, respectively. These observations can be interpreted as evidence of instantaneous and delayed dynamic triggering induced by large remote earthquakes. The maximum magnitude of the delayed triggered swarm increased with the strength (M_0/D) of the mega-earthquake and, the stronger the remote earthquake, the longer the delay time.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/71851, title ="Source Functions and Path Effects from Earthquakes in the Farallon Transform Fault Region, Gulf of California, Mexico that Occurred on October 2013", author = "Castro, Raúl R. and Stock, Joann M.", journal = "Pure and Applied Geophysics", volume = "174", number = "6", pages = "2239-2256", month = "June", year = "2017", doi = "10.1007/s00024-016-1346-4", issn = "0033-4553", url = "https://resolver.caltech.edu/CaltechAUTHORS:20161109-071414936", note = "© 2016 Springer International Publishing. \n\nReceived: 25 January 2016; Revised: 27 June 2016; Accepted: 29 June 2016; First Online: 09 July 2016. \n\nThe operation of the RESBAN network has been possible thanks to the financial support of the Mexican National Council for Science and Technology (CONACYT) (projects CB-2011-01-165401(C0C059), G33102-T and 59216). This paper was prepared while the first author (RRC) was on sabbatical year in Caltech. We thank Prof. Gurnis for the support provided. Dr. Lenin Avila-Barrientos facilitated part of the spectral records used to calculate the site functions. Antonio Mendoza Camberos pre-process the data from the RESBAN network and Arturo Perez Vertti maintains and operates the stations. We thank Dr. Edwards and the anonymous reviewer for their careful revisions, comments and suggestions which help us to improve the manuscript. We also acknowledge the Editor, Dr. Thomas H.W. Goebel.", revision_no = "18", abstract = "We determined source spectral functions, Q and site effects using regional records of body waves from the October 19, 2013 (M_w = 6.6) earthquake and eight aftershocks located 90 km east of Loreto, Baja California Sur, Mexico. We also analyzed records from a foreshock with magnitude 3.3 that occurred 47 days before the mainshock. The epicenters of this sequence are located in the south-central region of the Gulf of California (GoC) near and on the Farallon transform fault. This is one of the most active regions of the GoC, where most of the large earthquakes have strike–slip mechanisms. Based on the distribution of the aftershocks, the rupture propagated northwest with a rupture length of approximately 27 km. We calculated 3-component P- and S-wave spectra from ten events recorded by eleven stations of the Broadband Seismological Network of the GoC (RESBAN). These stations are located around the GoC and provide good azimuthal coverage (the average station gap is 39°). The spectral records were corrected for site effects, which were estimated calculating average spectral ratios between horizontal and vertical components (HVSR method). The site-corrected spectra were then inverted to determine the source functions and to estimate the attenuation quality factor Q. The values of Q resulting from the spectral inversion can be approximated by the relations Q_P =48.1±1.1f^(0.88±0.04) and Q_S =135.4±1.1f^(0.58±0.03) and are consistent with previous estimates reported by Vidales-Basurto et al. (Bull Seism Soc Am 104:2027–2042, 2014) for the south-central GoC. The stress drop estimates, obtained using the ω2 model, are below 1.7 MPa, with the highest stress drops determined for the mainshock and the aftershocks located in the ridge zone. We used the values of Q obtained to recalculate source and site effects with a different spectral inversion scheme. We found that sites with low S-wave amplification also tend to have low P-wave amplification, except for stations BAHB, GUYB and SFQB, located on igneous rocks, where the P-wave site amplification is higher.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/74487, title ="Seismic imaging of the metamorphism of young sediment into new crystalline crust in the actively rifting Imperial Valley, California", author = "Han, Liang and Hole, John A.", journal = "Geochemistry, Geophysics, Geosystems", volume = "17", number = "11", pages = "4566-4584", month = "November", year = "2016", doi = "10.1002/2016GC006610", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170223-074555793", note = "© 2016 American Geophysical Union. \n\nReceived 29 AUG 2016; Accepted 28 OCT 2016; Accepted article online 3 NOV 2016; Published online 18 NOV 2016. \n\nWe thank the Editor Thorsten Becker and three anonymous reviewers for their helpful and constructive reviews. This research was supported by NSF MARGINS and EarthScope grants 0742263 to J.A.H. and 0742253 to J.M.S., by the U. S. Geological Survey's Multihazards Research Program, and by the Southern California Earthquake Center (SCEC) (Contribution No. 6244). We thank the >90 field volunteers and USGS personnel who made data acquisition possible. Numerous landowners acknowledged in Rose et al. [2013] allowed access for shots and stations. Seismographs and technical support were provided by the IRIS-PASSCAL instrument facility; special thanks go to Mouse Reusch and Patrick Bastien from PASSCAL for their field and data efforts. Software support was provided by Landmark Software and Services, a Halliburton Company. The data have been archived at the IRIS DMC (http://ds.iris.edu/pic-ph5/metadata/SSIP/form.php).", revision_no = "10", abstract = "Plate-boundary rifting between transform faults is opening the Imperial Valley of southern California and the rift is rapidly filling with sediment from the Colorado River. Three 65–90 km long seismic refraction profiles across and along the valley, acquired as part of the 2011 Salton Seismic Imaging Project, were analyzed to constrain upper crustal structure and the transition from sediment to underlying crystalline rock. Both first arrival travel-time tomography and frequency-domain full-waveform inversion were applied to provide P-wave velocity models down to ∼7 km depth. The valley margins are fault-bounded, beyond which thinner sediment has been deposited on preexisting crystalline rocks. Within the central basin, seismic velocity increases continuously from ∼1.8 km/s sediment at the surface to >6 km/s crystalline rock with no sharp discontinuity. Borehole data show young sediment is progressively metamorphosed into crystalline rock. The seismic velocity gradient with depth decreases approximately at the 4 km/s contour, which coincides with changes in the porosity and density gradient in borehole core samples. This change occurs at ∼3 km depth in most of the valley, but at only ∼1.5 km depth in the Salton Sea geothermal field. We interpret progressive metamorphism caused by high heat flow to be creating new crystalline crust throughout the valley at a rate comparable to the ≥2 km/Myr sedimentation rate. The newly formed crystalline crust extends to at least 7–8 km depth, and it is shallower and faster where heat flow is higher. Most of the active seismicity occurs within this new crust.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/73138, title ="Continental rupture and the creation of new crust in the Salton Trough rift, Southern California and northern Mexico: Results from the Salton Seismic Imaging Project", author = "Han, Liang and Hole, John A.", journal = "Journal of Geophysical Research. Solid Earth", volume = "121", number = "10", pages = "7469-7489", month = "October", year = "2016", doi = "10.1002/2016JB013139", issn = "2169-9313", url = "https://resolver.caltech.edu/CaltechAUTHORS:20161222-100807138", note = "© 2016 American Geophysical Union. \n\nReceived 2 MAY 2016; Accepted 8 OCT 2016; Accepted article online 11 OCT 2016; Published online 30 OCT 2016. \n\nThis research was supported by NSF MARGINS and EarthScope grants 0742263 to J.A.H. and 0742253 to J.M.S., by NSF Marine Geology and Geophysics grant 0927446 to N.W.D. and G.M.K., by the U. S. Geological Survey's Multihazards Research Program, and by the Southern California Earthquake Center (SCEC) (contribution 6244). SCEC is funded by NSF cooperative agreement EAR-1033462 and USGS cooperative agreement G12AC20038. We thank the >90 field volunteers and USGS personnel who made data acquisition possible. Numerous landowners allowed access for shots and stations and are acknowledged in Rose et al. [2013]. Seismographs and technical support were provided by the IRIS-PASSCAL instrument facility; special thanks go to Mouse Reusch and Patrick Bastien from PASSCAL for their field and data efforts. We also thank the Associate Editor and two anonymous reviewers for their helpful and constructive reviews. The data have been archived at the IRIS DMC (ds.iris.edu/pic-ph5/metadata/SSIP/form.php).", revision_no = "11", abstract = "A refraction and wide-angle reflection seismic profile along the axis of the Salton Trough, California and Mexico, was analyzed to constrain crustal and upper mantle seismic velocity structure during active continental rifting. From the northern Salton Sea to the southern Imperial Valley, the crust is 17–18\u2009km thick and approximately one-dimensional. The transition at depth from Colorado River sediment to underlying crystalline rock is gradual and is not a depositional surface. The crystalline rock from ~3 to ~8\u2009km depth is interpreted as sediment metamorphosed by high heat flow. Deeper felsic crystalline rock could be stretched preexisting crust or higher-grade metamorphosed sediment. The lower crust below ~12\u2009km depth is interpreted to be gabbro emplaced by rift-related magmatic intrusion by underplating. Low upper mantle velocity indicates high temperature and partial melting. Under the Coachella Valley, sediment thins to the north and the underlying crystalline rock is interpreted as granitic basement. Mafic rock does not exist at 12–18\u2009km depth as it does to the south, and a weak reflection suggests Moho at ~28\u2009km depth. Structure in adjacent Mexico has slower midcrustal velocity, and rocks with mantle velocity must be much deeper than in the Imperial Valley. Slower velocity and thicker crust in the Coachella and Mexicali valleys define the rift zone between them to be >100\u2009km wide in the direction of plate motion. North American lithosphere in the central Salton Trough has been rifted apart and is being replaced by new crust created by magmatism, sedimentation, and metamorphism.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/69217, title ="Fault zone characteristics and basin complexity in the southern Salton Trough, California", author = "Persaud, Patricia and Ma, Yiran", journal = "Geology", volume = "44", number = "9", pages = "747-750", month = "September", year = "2016", doi = "10.1130/G38033.1", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160726-090423974", note = "© 2016 Geological Society of America. \n\nReceived 26 April 2016. Revision received 1 July 2016. Accepted 4 July 2016. \n\nWe thank P. Umhoefer, G. Axen, D. Scheirer, V. Langenheim, editor Bob Holdsworth, and an anonymous reviewer for their comments on the manuscript. The Salton Seismic Imaging Project (SSIP) was funded by the U.S. Geological Survey Multihazards Project, and the National Science Foundation Earthscope and Margins Programs through grants OCE-0742253 (to California Institute of Technology) and OCE-0742263 (to Virginia Polytechnic Institute and State University). Persaud was supported by U.S. Geological Survey grant G15AP00062.", revision_no = "13", abstract = "Ongoing oblique slip at the Pacific–North America plate boundary in the Salton Trough produced the Imperial Valley (California, USA), a seismically active area with deformation distributed across a complex network of exposed and buried faults. To better understand the shallow crustal structure in this region and the connectivity of faults and seismicity lineaments, we used data primarily from the Salton Seismic Imaging Project to construct a three-dimensional P-wave velocity model down to 8 km depth and a velocity profile to 15 km depth, both at 1 km grid spacing. A V_P = 5.65–5.85 km/s layer of possibly metamorphosed sediments within, and crystalline basement outside, the valley is locally as thick as 5 km, but is thickest and deepest in fault zones and near seismicity lineaments, suggesting a causative relationship between the low velocities and faulting. Both seismicity lineaments and surface faults control the structural architecture of the western part of the larger wedge-shaped basin, where two deep subbasins are located. We estimate basement depths, and show that high velocities at shallow depths and possible basement highs characterize the geothermal areas.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/69144, title ="Focal mechanisms and size distribution of earthquakes beneath the Krafla central volcano, NE Iceland", author = "Schuler, Juerg and Pugh, David J.", journal = "Journal of Geophysical Research. Solid Earth", volume = "121", number = "7", pages = "5152-5168", month = "July", year = "2016", doi = "10.1002/2016JB013213", issn = "2169-9313", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160720-154304105", note = "© 2016 American Geophysical Union. \n\nAccepted manuscript online: 18 July 2016; Manuscript Accepted: 12 July 2016; Manuscript Revised: 11 July 2016; Manuscript Received: 26 May 2016. Version of Record online: 28 Jul 2016. \n\nWe thank Julian Drew for the use of his CMM algorithm and Jon Tarasewicz for acquiring the bulk of the field data. Seismometers were borrowed from SEIS-UK under loan 891, with additional data from SIL network stations operated by the Icelandic Meteorological Office. The data will be stored at IRIS (www.iris.edu) and accessible from there. The Natural Environment Research Council UK funded the fieldwork. Landsvirkjun supported the field campaigns and provided borehole information. We thank two anonymous reviewers for critically reading this paper. J.S. also thanks Y. Kamer and S. Hiemer for discussing parts of their b-value method. Data were mainly processed using the ObsPy package and visualized using Matplotlib and Generic Mapping Tools. J.S. was supported by the Swiss National Science Foundation.", revision_no = "20", abstract = "Seismicity was monitored beneath the Krafla central volcano, NE Iceland, between 2009 and 2012 during a period of volcanic quiescence, when most earthquakes occured within the shallow geothermal field. The highest concentration of earthquakes is located close to the rock-melt transition zone as the IDDP-1 wellbore suggests, and decays quickly at greater depths. We recorded multiple swarms of microearthquakes, which coincide often with periods of changes in geothermal field operations, and found that about one third of the total number of earthquakes are repeating events. The event size distribution, evaluated within the central caldera, indicates average crustal values with b = 0.79 ± 0.04. No significant spatial b-value contrasts are resolved within the geothermal field nor in the vicinity of the drilled melt. Besides the seismicity analysis, focal mechanisms are calculated for 342 events. Most of these short-period events have source radiation patterns consistent with double-couple (DC) mechanisms. A few events are attributed to non-shear faulting mechanisms with geothermal fluids likely playing an important role in their source processes. Diverse faulting styles are inferred from DC events, but normal faulting prevails in the central caldera. The best-fitting compressional and tensional axes of DC mechanisms are interpreted in terms of the principal stress or deformation-rate orientations across the plate boundary rift. Maximum compressive stress directions are near-vertically aligned in different study volumes, as expected in an extensional tectonic setting. Beneath the natural geothermal fields, the least compressive stress axis is found to align with the regional spreading direction. In the main geothermal field both horizontal stresses appear to have similar magnitudes causing a diversity of focal mechanisms.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/70364, title ="Synchronous oceanic spreading and continental rifting in West Antarctica", author = "Davey, F. J. and Granot, R.", journal = "Geophysical Research Letters", volume = "43", number = "12", pages = "6162-6169", month = "June", year = "2016", doi = "10.1002/2016GL069087", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160915-090411864", note = "© 2016. American Geophysical Union. \n\nReceived 11 APR 2016; Accepted 31 MAY 2016; Accepted article online 3 JUN 2016; Published online 21 JUN 2016. \n\nThe aeromagnetic map in Figure 2 is available from F.F. and will be submitted to the NERC/BAS Polar Data Centre. Magnetic anomaly picks have been submitted to The Global Seafloor Fabric and Magnetic Lineation Data Base Project, link: http://www.soest.hawaii.edu/PT/GSFML/ML/index.html. The marine gravity data are available from GeoMap App, cruise NBP0701. The seismic data of Brancolini et al., 1995 are also available from the SCAR seismic Data Library System—http://sdls.ogs.trieste.it/. Sonobuoy data from NBP0701 are available from http://web.gps.caltech.edu/~clay/Adare_Sonobuoy/Adare_Sonobuoy.html). Adare Basin Sonobuoy data (2007), Sonobuoy Data from the Adare Basin, Antarctica. Caltech. Dataset. doi:10.7909/C37P8W9P. S.C. acknowledges funding from NSF grant OPP04-40959 and F.D. for funding from NZGSF. We acknowledge the critical reviews by John Behrendt and two anonymous reviewers that has greatly improved the paper. F.D. thanks Susan Ellis for advice.", revision_no = "17", abstract = "Magnetic anomalies associated with new ocean crust formation in the Adare Basin off north-western Ross Sea (43–26\u2009Ma) can be traced directly into the Northern Basin that underlies the adjacent morphological continental shelf, implying a continuity in the emplacement of oceanic crust. Steep gravity gradients along the margins of the Northern Basin, particularly in the east, suggest that little extension and thinning of continental crust occurred before it ruptured and the new oceanic crust formed, unlike most other continental rifts and the Victoria Land Basin further south. A preexisting weak crust and localization of strain by strike-slip faulting are proposed as the factors allowing the rapid rupture of continental crust.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/63757, title ="Seismic imaging of the shallow crust beneath the Krafla central volcano, NE Iceland", author = "Schuler, Juerg and Greenfield, Tim", journal = "Journal of Geophysical Research. Solid Earth", volume = "120", number = "10", pages = "7156-7173", month = "October", year = "2015", doi = "10.1002/2015JB012350", issn = "2169-9313", url = "https://resolver.caltech.edu/CaltechAUTHORS:20160119-093854474", note = "© 2015 American Geophysical Union. \n\nReceived 11 JUL 2015; Accepted 1 OCT 2015; Accepted article online 10 OCT 2015; Published online 30 OCT 2015. \n\nWe thank Julian Drew for use of his CMM location algorithm. Seismometers were provided by SEIS-UK under loan 891, with additional data from local SIL network stations kindly provided by the Icelandic Meteorological Office. The data will be stored at IRIS (www.iris.edu) and accessible from there. Funding was provided to R.S.W. by a grant from the Natural Environment Research Council and to T.G. from a Shell UK studentship. Landsvirkjun allowed us to use well information and assisted with logistics during our field campaigns. We are grateful to Sveinbjörn Steinþórsson, Heidi Soosalu, Janet Tibbitts, and the students who helped in the field. The figures were generated using the Generic Mapping Tools. We are grateful to S. Arnott for discussing his data set as well as R. Zierenberg and B. Kennedy for discussing their results on the quenched glasses from Krafla. We thank Páll Einarsson, Knútur Árnason, and the JGR Associate Editor for constructive comments. J.S. gratefully acknowledges support from the Swiss National Science Foundation, Department of Earth Sciences, Cambridge contribution number ESC.3491.", revision_no = "23", abstract = "We studied the seismic velocity structure beneath the Krafla central volcano, NE Iceland, by performing 3-D tomographic inversions of 1453 earthquakes recorded by a temporary local seismic network between 2009 and 2012. The seismicity is concentrated primarily around the Leirhnjúkur geothermal field near the center of the Krafla caldera. To obtain robust velocity models, we incorporated active seismic data from previous surveys. The Krafla central volcano has a relatively complex velocity structure with higher P wave velocities (V_p) underneath regions of higher topographic relief and two distinct low-V_p anomalies beneath the Leirhnjúkur geothermal field. The latter match well with two attenuating bodies inferred from S wave shadows during the Krafla rifting episode of 1974–1985. Within the Leirhnjúkur geothermalreservoir, we resolved a shallow (−0.5 to 0.5 km below sea level; bsl) region with low-V_p/V_s values and a deeper (0.5–1.5 km bsl) high-V_p/V_s zone. We interpret the difference in the velocity ratios of the two zones to be caused by higher rock porosities and crack densities in the shallow region and lower porosities and crack densities in the deeper region. A strong low-V_p/V_s anomaly underlies these zones, where a superheated steam zone within felsic rock overlies rhyolitic melt.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/57110, title ="Fault‐Slip Distribution of the 1999 M_w 7.1 Hector Mine Earthquake, California, Estimated from Postearthquake Airborne LiDAR Data", author = "Chen, T. and Akciz, S. O.", journal = "Bulletin of the Seismological Society of America", volume = "105", number = "2A", pages = "776-790", month = "April", year = "2015", doi = "10.1785/0120130108", issn = "0037-1106", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150430-094007973", note = "© 2015 Seismological Society of America.\n\nManuscript received 2 May 2013; Published Online 3 February 2015.\n\nThis research was supported by Public Service Funds for earthquake studies (201308012) and Fundamental Research Funds in the Institute of Geology (IGCEA1125). Tao Chen was sponsored as a visiting scholar to the U.S. Geological Survey (USGS) by the China Scholarship Council (Grant Number 2010419008). Work by D. Z. Zhang was supported, in part, by the Multi-Hazards Demonstration Project of the USGS. Jing Liu-Zeng and Kate Scharer helped us to improve the manuscript. We thank Katherine Kendrick for providing the database of field measurements from the original postearthquake observations of Treiman et al. (2002). We also thank an anonymous reviewer and Mike Oskin for their advice. Original LiDAR data acquisition was funded by the USGS and the Southern California Earthquake Center (SCEC). SCEC is funded by National Science Foundation Cooperative Agreement EAR-1033462 and USGS Cooperative AgreementG12AC20038. The SCEC contribution number for this article is 1973.", revision_no = "15", abstract = "The 16 October 1999 Hector Mine earthquake (M_w 7.1) was the first large earthquake for which postearthquake airborne Light Detection and Ranging (LiDAR) data were collected to image the fault surface rupture. In this work, we present measurements of both vertical and horizontal slip along the entire surface rupture of this earthquake based on airborne LiDAR data acquired in April 2000. We examine the details of the along‐fault slip distribution of this earthquake based on 255 horizontal and 85 vertical displacements using a 0.5 m digital elevation model derived from the LiDAR imagery. The slip measurements based on the LiDAR dataset are highest in the epicentral region, and taper in both directions, consistent with earlier findings by other works. The maximum dextral displacement measured from LiDAR imagery is 6.60±1.10\u2009\u2009m, located about 700 m south of the highest field measurement (5.25±0.85\u2009\u2009m). Our results also illustrate the difficulty in resolving displacements smaller than 1 m using LiDAR imagery alone. We analyze slip variation to see if it is affected by rock type and whether variations are statistically significant. This study demonstrates that a postearthquake airborne LiDAR survey can produce an along‐fault horizontal and vertical offset distribution plot of a quality comparable to a reconnaissance field survey. Although LiDAR data can provide a higher sampling density and enable rapid data analysis for documenting slip distributions, we find that, relative to field methods, it has a limited ability to resolve slip that is distributed over several fault strands across a zone. We recommend a combined approach that merges field observation with LiDAR analysis, so that the best attributes of both quantitative topographic and geological insight are utilized in concert to make best estimates of offsets and their uncertainties.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/54999, title ="A Crustal Velocity Model for the Southern Mexicali Valley, Baja California, Mexico", author = "Ramírez-Ramos, Erik E. and Vidal-Villegas, Antonio", journal = "Seismological Research Letters", volume = "86", number = "1", pages = "181-191", month = "January", year = "2015", doi = "10.1785/0220140007 ", issn = "0895-0695", url = "https://resolver.caltech.edu/CaltechAUTHORS:20150219-100201807", note = "© 2015 by the Seismological Society of America. Published Online 5 November 2014.\n\nThis project was the first of a bigger project designed to improve the estimation of the crustal model for the northern\nregion of Baja California. The Mexican National Council\nScience and Technology (Consejo Nacional de Ciencia y Tecnología [CONACYT], in Spanish) provided financial support\nfor this project (CB-2009-133019 SEP-CONACYT). J. Stock’s participation was supported by National Science Foundation\n(NSF) Grant OCE-0742253. This work was performed using the facilities of Centro de Investigación Científica y de\nEducación Superior de Ensenada (CICESE). José Acosta provided us the 2 Hz seismic stations deployed to record the explosion, and Gustavo Arellano and Euclides Ruíz provided the technical support for the SARA (http://www.sara.pg.it/scat.asp?idscat=17; last accessed October 2014) instrumentation. We acknowledge Luis Orozco, Oscar Gálvez, Francisco Méndez, Francisco Farfán, and Orlando Granados for their help in the installation of the instrumentation along the profile. Sergio Arregui provided the main script that we used for generating the maps using the Generic Mapping Tools (www.soest.hawaii.edu/gmt, last accessed October 2014; Wessel and Smith, 2009) software. We thank the RESNOM staff for the assistance in data accessibility (wave forms and location files) of the earthquakes used in this work. The comments and suggestions provided by Editor-in-Chief Zhigang Peng, Walter D. Mooney,\nand an anonymous reviewer substantially improved the content\nof this paper.", revision_no = "13", abstract = "In northern Baja California, the two largest regions with different geological characteristics are the granitic Peninsular Ranges of Baja California (PRBC) and the sedimentary environment of the Mexicali Valley (Lomnitz et al., 1970). The boundary of these two regions is the Main Gulf Escarpment (Fig. 1). The northern Baja California peninsula has active normal and strike‐slip faults originating from the transtensional limit between the Pacific and North America plates (Stock et al., 1991).", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/50049, title ="Deep crustal structure of the Adare and Northern Basins, Ross Sea, Antarctica, from sonobuoy data", author = "Selvans, M. M. and Stock, J. M.", journal = "Earth and Planetary Science Letters", volume = "405", pages = "220-230", month = "November", year = "2014", doi = "10.1016/j.epsl.2014.08.029", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140926-090020854", note = "© 2014 Elsevier B.V. \n\nReceived 8 March 2014;\nReceived in revised form 21 August 2014;\nAccepted 25 August 2014.\n\nWe thank F. Davey for helpful discussions of sonobuoy data analysis and interpretation, and K.S. Panter and an anonymous re-viewer for suggestions that improved the figures in this manuscript. We also thank Captain Mike Watson, the crew, and the Raytheon Polar Services Corporation technical staff on board the Nathaniel B. Palmer. This study was supported by National Science Foun-dation grants OPP04-40959 (S. Cande) and OPP-0440923 and OPP-0944711 (J. Stock and R. Clayton).", revision_no = "16", abstract = "Extension associated with ultraslow seafloor spreading within the Adare Basin, in oceanic crust just north of the continental shelf in the Ross Sea, Antarctica, extended south into the Northern Basin. Magnetic and gravity anomaly data suggest continuity of crustal structure across the continental shelf break that separates the Adare and Northern Basins. We use sonobuoy refraction data and multi-channel seismic (MCS) reflection data collected during research cruise NBP0701, including 71 new sonobuoy records, to provide constraints on crustal structure in the Adare and Northern Basins. Adjacent 1D sonobuoy profiles along several MCS lines reveal deep crustal structure in the vicinity of the continental shelf break, and agree with additional sonobuoy data that document fast crustal velocities (6000–8000 m/s) at shallow depths (1–6 km below sea level) from the Adare Basin to the continental shelf, a structure consistent with that of other ultraslow-spread crust. Our determination of crustal structure in the Northern Basin only extends through sedimentary rock to the basement rock, and so cannot help to distinguish between different hypotheses for formation of the basin.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/49226, title ="Assembly of a large earthquake from a complex fault system: Surface rupture kinematics of the 4 April 2010 El Mayor–Cucapah (Mexico) M_w 7.2 earthquake", author = "Fletcher, John M. and Teran, Orlando J.", journal = "Geosphere", volume = "10", number = "4", pages = "797-827", month = "August", year = "2014", doi = "10.1130/GES00933.1", issn = "1553-040X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140904-090345033", note = "© 2014 Geological Society of America. Received 25 March 2013. Revision received 18 March 2014. Accepted 25 April 2014. Published online 24 June 2014. This work was fi nanced by CONACYT (Consejo Nacional de Ciencia y Tecnología) grant 81463, SCEC (Southern California Earthquake Center) grant 1697, and National Science Foundation grant EAR-0529922; the GEER (Geotechnical Extreme Events Reconnaissance) Foundation provided funding for initial field work. S. Leprince was supported in part by the Keck Institute for Space Studies and by the Gordon\nand Betty Moore Foundation. Part of this study\nwas sponsored by the National Aeronautics and Space\nAdministration (NASA) Earth Surface and Interior\nfocus area and performed at the Jet Propulsion Laboratory,\nCalifornia Institute of Technology, under contract\nwith NASA. Enlightening discussions with Paul Wetmore\nand Francisco Suarez helped refine ideas about\ntectonics of the Big Bend domain and the kinematics\nof faulting in the Colorado River delta, respectively.\nWe thank John Galetzka, Kate Scharer, David Bowman,\nRoman Manjarrez, and Maria Oturno for help\nwith field work. We also thank Jose Mojarro, Sergio\nArregui, and Luis Gradilla for technical support.", revision_no = "32", abstract = "The 4 April 2010 moment magnitude (M_w) 7.2 El Mayor–Cucapah earthquake revealed the existence of a previously unidentified fault system in Mexico that extends ∼120 km from the northern tip of the Gulf of California to the U.S.–Mexico border. The system strikes northwest and is composed of at least seven major faults linked by numerous smaller faults, making this one of the most complex surface ruptures ever documented along the Pacific–North America plate boundary. Rupture propagated bilaterally through three distinct kinematic and geomorphic domains. Southeast of the epicenter, a broad region of distributed fracturing, liquefaction, and discontinuous fault rupture was controlled by a buried, southwest-dipping, dextral-normal fault system that extends ∼53 km across the southern Colorado River delta. Northwest of the epicenter, the sense of vertical slip reverses as rupture propagated through multiple strands of an imbricate stack of east-dipping dextral-normal faults that extend ∼55 km through the Sierra Cucapah. However, some coseismic slip (10–30 cm) was partitioned onto the west-dipping Laguna Salada fault, which extends parallel to the main rupture and defines the western margin of the Sierra Cucapah. In the northernmost domain, rupture terminates on a series of several north-northeast–striking cross-faults with minor offset (<8 cm) that cut uplifted and folded sediments of the northern Colorado River delta in the Yuha Desert.\n\nIn the Sierra Cucapah, primary rupture occurred on four major faults separated by one fault branch and two accommodation zones. The accommodation zones are distributed in a left-stepping en echelon geometry, such that rupture passed systematically to structurally lower faults. The structurally lowest fault that ruptured in this event is inclined as shallowly as ∼20°. Net surface offsets in the Sierra Cucapah average ∼200 cm, with some reaching 300–400 cm, and rupture kinematics vary greatly along strike. Nonetheless, instantaneous extension directions are consistently oriented ∼085° and the dominant slip direction is ∼310°, which is slightly (∼10°) more westerly than the expected azimuth of relative plate motion, but considerably more oblique to other nearby historical ruptures such as the 1992 Landers earthquake. Complex multifault ruptures are common in the central portion of the Pacific North American plate margin, which is affected by restraining bend tectonics, gravitational potential energy gradients, and the inherently three-dimensional strain of the transtensional and transpressional shear regimes that operate in this region.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/46519, title ="Community infrastructure and repository for marine magnetic identifications", author = "Seton, Maria and Whittaker, Joanne M.", journal = "Geochemistry, Geophysics, Geosystems", volume = "15", number = "4", pages = "1629-1641", month = "April", year = "2014", doi = "10.1002/2013GC005176", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140626-084743314", note = "© 2014 American Geophysical Union. \n\nReceived 25 November 2013; Accepted 16 January 2014; Accepted article online 22 January 2014; Published online 11 April 2014. \n\nWe would like to extend thanks to the many researchers who have directly or indirectly contributed magnetic anomaly identifications to the wider community and the NGDC for hosting the marine magnetic anomaly data sets. MS and JMW would like to thank support from Statoil, MS for support from Australian Research Council (ARC) grant DP0987713, RDM and SEW for support from ARC grant FL0992245, and PW for support from US National Science Foundation grant OCE-\n0752543. CG acknowledges the Geological Survey of Canada and\nGeological Survey of Norway for their support and access to digital magnetic databases. This research is supported by the Science and Industry Endowment Fund and also partly supported by the Research Council of Norway through its Centres of Excellence funding scheme, project number 223272.", revision_no = "18", abstract = "Magnetic anomaly identifications underpin plate tectonic reconstructions and form the primary data set from which the age of the oceanic lithosphere and seafloor spreading regimes in the ocean basins can be determined. Although these identifications are an invaluable resource, their usefulness to the wider scientific community has been limited due to the lack of a central community infrastructure to organize, host, and update these interpretations. We have developed an open-source, community-driven online infrastructure as a repository for quality-checked magnetic anomaly identifications from all ocean basins. We provide a global sample data set that comprises 96,733 individually picked magnetic anomaly\nidentifications organized by ocean basin and publication reference, and provide accompanying Hellingerformat\nfiles, where available. Our infrastructure is designed to facilitate research in plate tectonic reconstructions or research that relies on an assessment of plate reconstructions, for both experts and nonexperts alike. To further enhance the existing repository and strengthen its value, we encourage others in the community to contribute to this effort.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44628, title ="Active Pacific North America Plate boundary tectonics as evidenced by seismicity in the oceanic lithosphere offshore Baja California, Mexico", author = "Hauksson, Egill and Kanamori, Hiroo", journal = "Geophysical Journal International", volume = "196", number = "3", pages = "1619-1630", month = "March", year = "2014", doi = "10.1093/gji/ggt467", issn = "0956-540X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140403-094603730", note = "© 2013 Authors. Published by Oxford University Press on behalf of The Royal Astronomical Society. Accepted 2013 November 15. Received 2013 November 14; in original form 2013 April 4. First published online: December 19, 2013. We thank C. Sorlien and L. Jones for helpful discussions and the personnel of the USGS/Caltech SCSN and the Southern California Earthquake Data Center (SCEDC) for data collection and distribution. The IRIS DMS data center was used to access the seismic data from GSN and FDSN stations. EH was supported by NEHRP/USGS grant G13AP00047. This research was also supported by the Southern California Earthquake Center, which is funded by NSF Cooperative\nAgreement EAR-0529922 and USGS Cooperative Agreement\n07HQAG0008. This paper is SCEC contribution # 1745 and contribution\n# 10089 of Division of Geological and Planetary Sciences,\nCalifornia Institute of Technology, Pasadena, CA.", revision_no = "16", abstract = "Pacific Ocean crust west of southwest North America was formed by Cenozoic seafloor spreading between the large Pacific Plate and smaller microplates. The eastern limit of this seafloor, the continent–ocean boundary, is the fossil trench along which the microplates subducted and were mostly destroyed in Miocene time. The Pacific–North America Plate boundary motion today is concentrated on continental fault systems well to the east, and this region of oceanic crust is generally thought to be within the rigid Pacific Plate. Yet, the 2012 December 14 M_w 6.3 earthquake that occurred about 275\u2009km west of Ensenada, Baja California, Mexico, is evidence for continued tectonism in this oceanic part of the Pacific Plate. The preferred main shock centroid depth of 20\u2009km was located close to the bottom of the seismogenic thickness of the young oceanic lithosphere. The focal mechanism, derived from both teleseismic P-wave inversion and W-phase analysis of the main shock waveforms, and the 12 aftershocks of M ∼3–4 are consistent with normal faulting on northeast striking nodal planes, which align with surface mapped extensional tectonic trends such as volcanic features in the region. Previous Global Positioning System (GPS) measurements on offshore islands in the California Continental Borderland had detected some distributed Pacific and North America relative plate motion strain that could extend into the epicentral region. The release of this lithospheric strain along existing zones of weakness is a more likely cause of this seismicity than current thermal contraction of the oceanic lithosphere or volcanism. The main shock caused weak to moderate ground shaking in the coastal zones of southern California, USA, and Baja California, Mexico, but the tsunami was negligible. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/46258, title ="The Ayyubid Orogen: An Ophiolite Obduction-Driven Orogen in the Late Cretaceous of the Neo-Tethyan South Margin", author = "Şengör, A. M. Celâl and Stock, Joann", journal = "Geoscience Canada", volume = "41", pages = "225-254", month = "January", year = "2014", doi = "10.12789/geocanj.2014.41.042", issn = "0315-0941", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140613-081909428", note = "© 2014 GAC/AGC®.\n\nReceived July 2013;\nAccepted as revised January 2014.\n\nWe are extremely pleased and honoured\nto contribute this paper in memory\nof a great geologist, Professor\nHarold (‘Hank’) Williams, a master of\nophiolite geology, among other subjects.\nFor Şengör, the pleasure and\nhonour are related to a long friendship\nwith Professor Williams. Williams was\namong his earliest field instructors.\nWhen Şengör was only a second-year\nstudent, his teacher John F. Dewey sent\nhim to work under Williams and W.S.F.\nKidd for a month in Newfoundland.\nThat was his first encounter with ophiolites\nin the field. That initial acquaintance\nturned into a life-long friendship,\nduring which he continued to learn\nfrom Williams. We thank Jim Hibbard,\nwho was the other student with Şengör\nduring that memorable field work in\nNewfoundland, for inviting us to contribute\nto the Williams’ memorial volume.\nŞengör’s friends in Libya, especially\nEmin Yanılmaz and Ali El-Arnauti, who took him around in\nCyrenaica, showed him the critical outcrops\nand provided him with a massive\namount of literature, probably would\nhave been co-authors in this paper, had\nthe unfortunate events that befell both\nLibya and Syria not led to his losing\ntheir tracks. We heard that Emin Yanılmaz\nsafely left Syria to return to\nTurkey, but we have not been able to\nget any news of Ali El-Arnauti. We\ncan only hope that he managed to survive\nsafely the destruction of his country.\nProfessor Hubert Whitechurch\nkindly supplied us with a pre-print of\nhis important new paper on the Kermanshah\nophiolites in Iran and Professor\nLeigh H. Royden discussed with us\nher work with Oliver Jagoutz in the\nHimalayan Neo-Tethys that much\nencouraged us in our interpretations.\nShe was also helpful in evaluating the\nLibyan gravity anomalies. Professor Ali\nPolat helped with literature research in\nCanada. We thank Professors Brian P.\nWernicke , B. Clark Burchfiel and an\nanonymous reviewer for a critical reading\nof an earlier draft of this paper.\nJim Hibbard, the guest editor of\nHank’s volume and Brendan Murphy,\nthe editor-in-chief of Geoscience Canada\nalso made us work hard to make our\npresentation clearer. We thank Cindy\nMurphy for her great assistance during\nthe final production of the paper.", revision_no = "11", abstract = "A minimum 5000-km long obduction-driven orogeny of medial to late Cretaceous age is located between Cyrenaica in eastern Libya and Oman. It is herein called the Ayyubid Orogen after the Ayyubid Empire that covered much of its territory. The Ayyubid orogen is distinct from other Alpide orogens and has two main parts: a western, mainly germanotype belt and an eastern mainly alpinotype belt. The germanotype belt formed largely as a result of an aborted obduction, whereas the alpinotype part formed as a result of successful and large-scale obduction events that choked a nascent subduction zone. The mainly germanotype part coincides with Erich Krenkel's Syrian Arc (Syrischer Bogen) and the alpinotype part with Ricou's Peri-Arabian Ophiolitic Crescent (Croissant Ophiolitique péri-Arabe). These belts formed as a consequence of the interaction of one of the now-vanished Tethyan plates and Afro-Arabia. The Africa-Eurasia relative motion has influenced the orogen's evolution, but was not the main causative agent. Similar large and complex obduction-driven orogens similar to the Ayyubids may exist along the Ordovician Newfoundland/Scotland margin of the Caledonides and along the Ordovician European margin of the Uralides.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/37915, title ="Report on the August 2012 Brawley Earthquake Swarm in Imperial Valley, Southern California", author = "Hauksson, Egill and Stock, Joann", journal = "Seismological Research Letters", volume = "84", number = "2", pages = "177-189", month = "March", year = "2013", doi = "10.1785/0220120169", issn = "0895-0695", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130412-114502163", note = "© 2013 Seismological Society of America. \n\nWe thank the personnel of the United States Geological Survey (USGS)–California Institute of Technology (Caltech)\nSouthern California Seismic Network (SCSN) for picking the\narrival times and archiving the seismograms and the Southern\nCalifornia Earthquake Data Center for distributing the data.\nTerraSAR-X data are copyright 2012 DLR and were provided\nunder the Group on Earth Observation (GEO) Geohazard\nSupersite program project prlund_GEO0927. E. Hauksson and W. Yang were supported by the National Earthquake Hazards Reduction Program/USGS Grant 12HQPA0001. This research was also supported by the Southern California Earthquake Center (SCEC), which is funded by National Science Foundation (NSF) Cooperative Agreement EAR-0529922 and USGS Cooperative Agreement 07HQAG0008. This paper is Contribution 1678 of SCEC and Contribution 10083 of the Division of Geological and Planetary Sciences, Caltech, Pasadena, California. We thank K. Marty (Imperial Valley College) and S. Williams (consulting geologist from Imperial, California) for help with fieldwork. The high-rate GPS data were processed and provided by S. Owen from the Jet Propulsion Laboratory (JPL). Part of this research was supported by the National Aeronautics and Space Administration (NASA) Earth Surface and Interior focus area and performed at the JPL, Caltech. We thank G. Fuis and D. Hill for reviews and J. Hole for valuable\ndiscussions about the tectonics and velocity structure. J. Stock’s participation was supported by NSF Grant OCE-0742253. The University of California at Santa Barbara operates the Wildlife Liquefaction Array facility, with funding through the George E. Brown, Jr., Network for Earthquake Engineering Simulation program of the NSF under Award CMMI-0927178. Most figures were done using GMT (Wessel and Smith, 1998). ", revision_no = "37", abstract = "The 2012 Brawley earthquake swarm occurred in the Brawley Seismic Zone (BSZ) within the Imperial Valley of southern California (Fig. 1). The BSZ is the northernmost extensional segment of the Pacific–North America plate boundary system. Johnson and Hill (1982) used the distribution of seismicity since the 1930s to outline the geographical extent of the BSZ, defining boundaries of the BSZ as shown in Figure 1. Its north–south extent ranges from the northern section of the Imperial fault, starting approximately 10 km north of the United States–Mexico international border and connecting to the southern end of the San Andreas fault, where it terminates in the Salton Sea. Larsen and Reilinger (1991), who defined a similar geographical extent of the BSZ, argued that the BSZ was migrating to the northwest, which they associated with the propagation of the Gulf of California rift system into the North American continent. During the seismically active period of the 1970s, the BSZ produced close to half of the earthquakes recorded in California (Johnson and Hill, 1982; Hutton et al., 2010). However, for two decades following the 1979 Imperial Valley mainshock M_w 6.4 and its aftershock sequence, the BSZ was much less active. In general, the BSZ seismicity is indicative of right-lateral strike-slip plate motion accompanied by crustal thinning as well as possible associated fluid movements in the crust (Chen and Shearer, 2011). The 2012 Brawley swarm produced more than 600 events recorded by the United States Geological Survey (USGS)–California Institute of Technology (Caltech) Southern California Seismic Network (SCSN). Other monitoring instruments in the region, such as the Global Positioning System (GPS) network, creepmeters, and the Wildlife Liquefaction Array (WLA) also recorded signals from the largest events. In addition, Interferometric Synthetic Aperture Radar (InSAR) satellites collected images from space. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/38544, title ="Revised Eocene-Oligocene kinematics for the West Antarctic rift system", author = "Granot, R. and Cande, S. C.", journal = "Geophysical Research Letters", volume = "40", number = "2", pages = "279-284", month = "January", year = "2013", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20130516-133349919", note = "© 2012 American Geophysical Union. \n\nReceived 9 October 2012; revised 14 November 2012; accepted 20 November 2012; published 31 January 2013.\n\nWe would like to thank Graeme Eagles and an anonymous reviewer for their constructive reviews. This study was\nfunded by NSF grants OPP04-40959 (SIO) and OPP04-40923 (Caltech).", revision_no = "20", abstract = "Past plate motion between East and West Antarctica along the West Antarctic rift system had important regional and global implications. Although extensively studied, the kinematics of the rift during Eocene-Oligocene time still remains elusive. Based on a recent detailed aeromagnetic survey from the Adare and Northern Basins, located in the northwestern Ross Sea, we present the first well-constrained kinematic model with four rotations for Anomalies 12o, 13o, 16y, and 18o (26.5–40.13\u2009Ma). These rotation poles form a cluster suggesting a stable sense of motion during that period of time. The poles are located close to the central part of the rift implying that the local motion varied from extension in the western Ross Sea sector (Adare Basin, Northern Basin, and Victoria Land Basin) to dextral transcurrent motion in the Ross Ice Shelf and to oblique convergence in the eastern end of the rift zone. The results confirm previous estimates of 95\u2009km of extension in the Victoria Land Basin.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/43122, title ="Geochemistry of the extensive peralkaline pyroclastic flow deposit of NW Mexico, based on conventional and handheld X-ray fluorescence. Implications in a regional context", author = "Vidal-Solano, J. R. and Lozano Santa Cruz, R.", journal = "Journal of Iberian Geology", volume = "39", number = "1", pages = "121-130", month = "January", year = "2013", doi = "10.5209/rev_JIGE.2013.v39.n1.41754", issn = "1698-6180", url = "https://resolver.caltech.edu/CaltechAUTHORS:20131220-135844497", note = "© 2013 Universidad Complutense de Madrid.\n\nReceived: April 26, 2011; Accepted: April 12, 2013.\n\nThis work was supported by a Research Grant #061198\nfrom Consejo Nacional de Ciencia y Tecnología (CONACYT)\nto Jesús Roberto Vidal Solano. Thanks to Sheila A.\nCorrales (Departamento de Geología de la Universidad\nde Sonora) for thin-section and rock slab preparation. J.\nStock’s participation was supported by the US National\nScience Foundation grant EAR-0911761. The authors\nwish to thank reviewers Dr. Takeshi Kuritani and Dr.\nManoj. K. Pandit for valuable comments that have enriched\nthis work. Likewise, the detailed and careful comments\nof Dr. Alain Demant are greatly appreciated.", revision_no = "11", abstract = "Chemical analyses conducted on the surface of rock slabs under a combination of two X-ray spectrometry methods, wavelength dispersive XRF and energy dispersive XRF, are used to establish a geochemical correlation between the studied samples. This proves to be an excellent method for the characterization of volcanic glasses, particularly when particles of exotic origin are present, because the effect of these is not easily eliminated by conventional whole rock analysis. Analyses of glassy rhyolites (ignimbrites and lava flows) in northwestern Mexico establish a geochemical signature for the samples, providing criteria that allow us to: a) correlate them with a peralkaline volcanic event, previously reported, that occurred during Middle Miocene time; b) distinguish them from other metaluminous varieties in the region and, c) propose a correlation between all the peralkaline vitrophyres that crop out within the studied area, of at least 50.000 km^2, validating the hypothesis that they are related to the same volcanic event. Finally, based on the results of this study and previous geological investigations, it is proposed that a distance of more than 100 km between the geographical location of the thickest peralkaline deposits in Sonora, is probably related to a displacement along transtensional dextral faults during the Late Miocene.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/41688, title ="Petrografía, geoquímica, petrofábrica y paleomagnetismo de la Toba de San Felipe en la región de Cataviña, Baja California, México", author = "Olguín-Villa, Angel Enrique and Vidal-Solano, Jesús Roberto", journal = "Revista Mexicana de Ciencias Geológicas", volume = "30", number = "2", pages = "282-298", month = "January", year = "2013", issn = "1026-8774", url = "https://resolver.caltech.edu/CaltechAUTHORS:20131004-131249954", note = "© 2013 Universidad Nacional Autónoma de México.\n\nManuscrito recibido: Febrero 26, 2013;\nManuscrito corregido recibido: Abril 2, 2013; Manuscrito aceptado: Junio 1, 2013.\n\nEste trabajo deriva de la tesis de licenciatura del primer\nautor y forma parte de los proyectos de Ciencia Básica\nCONACYT: 1) #61198 “Estudio de los Mecanismos\nEruptivos y de la Petrogénesis del Volcanismo Hiperalcalino\nen el NW de México (Sonora y Baja California)” y, 2)\n#180784 “Evolución Geodinámica del Proto-Golfo de\nCalifornia: Énfasis en los vestigios volcánicos del Mioceno\nen Sonora, México.”, que financiaron también estancias de\ninvestigación en el extranjero. El primer autor agradece\nal titular de los proyectos mencionados, el Dr. Jesús\nRoberto Vidal Solano, por la dirección de este trabajo y\ntodo el apoyo brindado durante los pasados tres años y a\nla Dra. Joann M. Stock por la codirección de la tesis de\nlicenciatura, investigación que fue también favorecida por\nlos proyectos NSF EAR 0911761 y NSF EAR 0610011. Se\nagradece también al Dr. Alain Demant y a los árbitros Dr.\nLuis Alva Valdivia y Dr. Jose Luis Arce por sus atinadas\nobservaciones y valiosas correcciones. Así mismo a la gente\nde los laboratorios de Paleomagnetismo (Paleomagnetics\nLaboratory) y Sismología (Seismological Laboratory)\ndel Instituto Tecnológico de California (Caltech) por\nsu hospitalidad durante las estancias de investigación\nrealizadas durante los veranos de los años 2008 y 2009; a\nmis compañeros de licenciatura Ricardo Enrique Ortega\nOchoa, Alejandra Marisela Gómez Valencia, Elizard\nGonzález Becuar, al Quim. Pablo Peñaflor Escárcega por\nsu amabilidad y disposición para la preparación de las\nmuestras en el laboratorio de trituración y pulverizado de\nla Estación Regional del Noroeste, UNAM. Al Dr. Carlos Pallares por su valiosa experiencia, orientación y consejos\npara el trabajo de campo en B.C. Se agradece por fin la\nhospitalidad y servicios prestados por el RV park San\nAgustín, en San Agustín, Baja California.", revision_no = "12", abstract = "A pyroclastic density current deposit has been recognized within the middle Miocene sequences\nin the Cataviña region, Baja California. The rhyolitic deposit is a poorly welded ignimbrite and has\nreduced thicknesses (<30 m), corresponding to distal facies from the source area. The mineral assemblage\nsanidine>green clinopyroxene>fayalite is analogous to that of all ignimbrite deposits of this nature in\nnorthwestern Mexico. Geochemical studies emphasize, first, the peralkaline character defining a comendite\nvariety for the rhyolitic magma, and second, that higher concentrations of Sr and Ba are distinctive features\nof the Cataviña ignimbrite, which are related to the incorporation of xenocrysts during its emplacement.\nPaleomagnetic and geochemical studies correlate this deposit with the Tuff of San Felipe-Ignimbrite of\nHermosillo (TSF-IGH). These outcrops represent the westernmost remains of the TSF-IGH event in NW\nMexico and the southernmost outcrops in Baja California. The isopach map, petrofabric and magnetic\nfabric results of this work make possible a model for the TSF-IGH emplacement, which considers that\nthe pyroclastic flow came from Sonora invading the area from east to west.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/35738, title ="The 2012 Sumatra great earthquake sequence", author = "Duputel, Zacharie and Kanamori, Hiroo", journal = "Earth and Planetary Science Letters", volume = "351", pages = "247-257", month = "October", year = "2012", doi = "10.1016/j.epsl.2012.07.017", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20121130-081922437", note = "© 2012 Elsevier B.V.\n\nAccepted 15 July 2012. Available online 1 September 2012. \nEditor: P. Shearer.\n\nWe thank Shengji Wei, Don Helmberger, Thorne Lay and two anonymous reviewers for helpful discussions. This work uses Federation of Digital Seismic Networks (FDSN) seismic data and CMT solutions from the Global CMT catalog. The Incorporated Research Institutions for Seismology (IRIS) Data Management System (DMS) was used to access the data. This work made use of the Matplotlib python library, of the Basemap toolkit and of the neighbourhood algorithm sampler developed by Malcolm Sambridge. Lingsen Meng and Jean-Paul Ampuero were supported by NSF Grant EAR-1015704.", revision_no = "23", abstract = "The equatorial Indian Ocean is a well known place of active intraplate deformation defying the conventional view of rigid plates separated by narrow boundaries where deformation is confined. On 11 April 2012, this region was hit in a couple of hours by two of the largest strike-slip earthquakes ever recorded (moment magnitudes Mw=8.6 and 8.2). Broadband seismological observations of the Mw=8.6 mainshock indicate a large centroid depth (∼30 km) and remarkable rupture complexity. Detailed study of the surface-wave directivity and moment rate functions clearly indicates the partition of the rupture into at least two distinct subevents. To account for these observations, we developed a procedure to invert for multiple-point-source parameters. The optimum source model at long period consists of two point sources separated by about 209 km with magnitudes Mw=8.5 and 8.3. To explain the remaining discrepancies between predicted and observed surface waves, we can refine this model by adding directivity along the WNW–ESE axis. However, we do not exclude more complicated models. To analyze the Mw=8.2 aftershock, we removed the perturbation due to large surface-wave arrivals of the Mw=8.6 mainshock by subtracting the corresponding synthetics computed for the two-subevent model. Analysis of the surface-wave amplitudes suggests that the Mw=8.2 aftershock had a large centroid depth between 30 km and 40 km. This major earthquake sequence brings a new perspective to the seismotectonics of the equatorial Indian Ocean and reveals active deep lithospheric deformation.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/33251, title ="Earthquake in a Maze: Compressional Rupture Branching During the 2012 M_w 8.6 Sumatra Earthquake", author = "Meng, L. and Ampuero, J.-P.", journal = "Science", volume = "337", number = "6095", pages = "724-726", month = "August", year = "2012", doi = "10.1126/science.1224030", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120816-082822417", note = "© 2012 American Association for the Advancement of Science. Received 30 April 2012; accepted 5 July 2012.\nPublished Online July 19 2012.\nThis research was supported by NSF\ngrant EAR-1015704, by the Gordon and Betty Moore\nFoundation, and by the Southern California Earthquake Center\n(SCEC), which is funded by NSF Cooperative Agreement\nEAR-0106924 and USGS Cooperative Agreement 02HQAG0008.\nThe Japanese Hi-net (www.hinet.bosai.go.jp) and the European\nORFEUS (www.orfeus-eu.org) data centers were used to\naccess the broadband seismograms. The magnetic anomalies\nare from the EMAG2 database available at the National\nGeophysical Data Center (www.ngdc.noaa.gov). The satellite\ngravity anomaly data are from the UCSD TOPEX v. 18.1\ndatabase. The multibeam bathymetry from the KNOX06RR\ncruise is available at Marine Geoscience Data System\n(www.marine-geo.org). We thank R.-C. Lien and B. Ma\nfor providing the Roger Revelle (RR1201) multibeam data\nfrom the DYNAMO cruise. We thank H. Kanamori for\nvaluable discussions about this event. This paper is Caltech\nTectonics Observatory contribution 215, Caltech Seismo Lab\ncontribution 10078, and SCEC contribution 1656.", revision_no = "30", abstract = "Seismological observations of the 2012 moment magnitude 8.6 Sumatra earthquake reveal unprecedented complexity of dynamic rupture. The surprisingly large magnitude results from the combination of deep extent, high stress drop, and rupture of multiple faults. Back-projection source imaging indicates that the rupture occurred on distinct planes in an orthogonal conjugate fault system, with relatively slow rupture speed. The east-southeast–west-northwest ruptures add a new dimension to the seismotectonics of the Wharton Basin, which was previously thought to be controlled by north-south strike-slip faulting. The rupture turned twice into the compressive quadrant, against the preferred branching direction predicted by dynamic Coulomb stress calculations. Orthogonal faulting and compressional branching indicate that rupture was controlled by a pressure-insensitive strength of the deep oceanic lithosphere.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/30067, title ="Using overlapping sonobuoy data from the Ross Sea to construct a 2D deep crustal velocity model", author = "Selvans, M. M. and Clayton, R. W.", journal = "Marine Geophysical Research", volume = "33", number = "1", pages = "17-32", month = "March", year = "2012", doi = "10.1007/s11001-011-9143-z", issn = "0025-3235", url = "https://resolver.caltech.edu/CaltechAUTHORS:20120412-132057738", note = "© 2011 Springer Science+Business Media B.V.\nReceived: 13 June 2011; Accepted: 1 December 2011; Published online: 20 December 2011.\nWe would like to thank Captain Mike Watson,\nthe crew, and the Raytheon Polar Services Corporation technical staff\non board the Nathaniel B. Palmer. This study was supported by\nNational Science Foundation grants OPP04-40959 (S. Cande) and\nOPP-0440923 and OPP-0944711 (J. Stock and R. Clayton).", revision_no = "16", abstract = "Sonobuoys provide an alternative to using long streamers while conducting multi-channel seismic (MCS) studies, in order to provide deeper velocity control. We present analysis and modeling techniques for interpreting the sonobuoy data and illustrate the method with ten overlapping sonobuoys collected in the Ross Sea, offshore from Antarctica. We demonstrate the importance of using the MCS data to correct for ocean currents and changes in ship navigation, which is required before using standard methods for obtaining a 1D velocity profile from each sonobuoy. We verify our 1D velocity models using acoustic finite-difference (FD) modeling and by performing depth migration on the data, and demonstrate the usefulness of FD modeling for tying interval velocities to the shallow crust imaged using MCS data. Finally, we show how overlapping sonobuoys along an MCS line can be used to construct a 2D velocity model of the crust. The velocity model reveals a thin crust (5.5 ± 0.4 km) at the boundary between the Adare and Northern Basins, and implies that the crustal structure of the Northern Basin may be more similar to that of the oceanic crust in the Adare Basin than to the stretched continental crust further south in the Ross Sea.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/24616, title ="Constraints on Jalisco Block Motion and Tectonics of the Guadalajara Triple Junction from 1998–2001 Campaign GPS Data", author = "Selvans, Michelle M. and Stock, Joann M.", journal = "Pure and Applied Geophysics", volume = "168", number = "8-9", pages = "1435-1447", month = "August", year = "2011", issn = "0033-4553", url = "https://resolver.caltech.edu/CaltechAUTHORS:20110801-133119672", note = "© 2011 Springer Basel AG.\n\nReceived February 10, 2010, revised July 10, 2010, accepted September 28, 2010, Published online November 9, 2010.\n\nWe would like to thank Jeff Genrich and Tom Herring for helpful discussions. Support for this research was provided by National Science Foundation grants EAR-0510395 (J. Stock) and EAR-0510553 (C. DeMets).", revision_no = "16", abstract = "A GPS campaign network in the state of Jalisco was\noccupied for ~36 h per station most years between 1995 and\n2005; we use data from 1998–2001 to investigate tectonic motion and interseismic deformation in the Jalisco area with respect to the North America plate. The twelve stations used in this analysis provide coverage of the Jalisco Block and adjacent North America plate, and show a pattern of motion that implies some contribution to Jalisco Block boundary deformation from both tectonic motion\nand interseismic deformation due to the offshore 1995 earthquake. The consistent direction and magnitude of station motion on the Jalisco Block with respect to the North America reference frame, ~2 mm/year to the southwest (95% confidence level), perhaps can be attributed to tectonic motion. However, some station velocities within and across the boundaries of the Jalisco Block are also non-zero (95% confidence level), and the overall pattern of\nstation velocities indicates both viscoelastic response to the 1995 earthquake and partial coupling of the subduction interface (together termed \"interseismic deformation\"). Our results show motion across the northern Colima rift, the eastern boundary of the Jalisco Block, which is likely to be sinistral oblique extension rather than pure extension. We constrain extension across both the Colima rift and the northeastern boundary of the Jalisco Block, the Tepic-\nZacoalco rift, to ≤8 mm/year (95% confidence level), slow compared to relative rates of motion at nearby plate boundaries.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/24602, title ="Double-difference Relocation of the Aftershocks of the Tecomán, Colima, Mexico Earthquake of 22 January 2003", author = "Andrews, Vanessa and Stock, Joann", journal = "Pure and Applied Geophysics", volume = "168", number = "8-9", pages = "1331-1338", month = "August", year = "2011", issn = "0033-4553", url = "https://resolver.caltech.edu/CaltechAUTHORS:20110801-073428119", note = "© 2010 The Author(s). \nThis article is distributed under the terms of the\nCreative Commons Attribution Noncommercial License which\npermits any noncommercial use, distribution, and reproduction in\nany medium, provided the original author(s) and source are\ncredited.\n\nReceived 12 February 2010; Revised: 6 August 2010; Accepted: 9 August 2010; Published online: 10 November 2010. Research supported by the US National Science\nFoundation under grant EAR-0510395 and by the\nCalifornia Institute of Technology’s division of\nGeological and Planetary Sciences under contribution\n10051.", revision_no = "24", abstract = "On 22 January 2003, the M_w = 7.6 Tecomán earthquake struck offshore of the state of Colima, Mexico, near the diffuse triple junction between the Cocos, Rivera, and North American plates. Three-hundred and fifty aftershocks of the Tecomán earthquake with magnitudes between 2.6 and 5.8, each recorded by at least 7 stations, are relocated using the double difference method. Initial locations are determined using P and S readings from the Red Sismológica Telemétrica del Estado de Colima (RESCO) and a 1-D velocity model. Because only eight RESCO stations were operating immediately following the Tecomán earthquake, uncertainties in the initial locations and depths are fairly large, with average uncertainties of 8.0 km in depth and 1.4 km in the north–south and east–west directions. Events occurring between 24 January and 31 January were located using not only RESCO phase readings but also additional P and S readings from 11 temporary stations. Average uncertainties decrease to 0.8 km in depth, 0.3 km in the east–west direction, and 0.7 km in the north–south direction for events occurring while the temporary stations were deployed. While some preliminary studies of the early aftershocks suggested that they were dominated by shallow events above the plate interface, our results place the majority of aftershocks along the plate interface, for a slab dipping between approximately 20° and 30°. This is consistent with the slab positions inferred from geodetic studies. We do see some upper plate aftershocks that may correspond to forearc fault zones, and faults inland in the upper plate, particularly among events occurring more than 3 months after the mainshock.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/24633, title ="The 2010 M_w 7.2 El Mayor-Cucapah Earthquake Sequence, Baja California, Mexico and Southernmost California, USA: Active Seismotectonics along the Mexican Pacific Margin", author = "Hauksson, Egill and Stock, Joann", journal = "Pure and Applied Geophysics", volume = "168", number = "8-9", pages = "1255-1277", month = "August", year = "2011", doi = "10.1007/s00024-010-0209-7", issn = "0033-4553", url = "https://resolver.caltech.edu/CaltechAUTHORS:20110802-141212219", note = "© 2010 Springer Basel AG. \n\nReceived July 10, 2010, revised September 1, 2010, accepted September 6, 2010, Published online November 16, 2010. \n\nThis research was supported by the US Geological Survey Grant G10AP00017; NSF grants EAR-0911761 and OCE-0742253 to Caltech, and by the Southern California Earthquake Center. SCEC is funded by NSF Cooperative Agreement EAR-0529922 and USGS Cooperative Agreement 07HQAG0008. The Incorporated Research Institutions for Seismology (IRIS) Data Management System (DMS) was used to access the Global Seismographic Network data. Funds for maintenance of RESNOM network are provided by CICESE. We thank S. Wei, S. Skinner, and E. Glowacka for feedback and discussions. We thank L. Munguía, G. Diaz, F. Farfan, I. Mendez, L. Orozco, O. Galvez, and S. Arregui, Department of Seismology, CICESE, Baja California, Mexico, and N. Scheckel, A. Guarino, and B. Wu of the SCSN for help with data collection and processing. Most figures were done using GMT (WESSEL and SMITH, 1998). SCEC contribution number 1,439. Contribution number 10,047, Seismological Laboratory, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena.", revision_no = "26", abstract = "The El Mayor-Cucapah earthquake sequence started with a few foreshocks in March 2010, and a second sequence of 15 foreshocks of M > 2 (up to M4.4) that occurred during the 24 h preceding the mainshock. The foreshocks occurred along a north–south trend near the mainshock epicenter. The M_w 7.2 mainshock on April 4 exhibited complex faulting, possibly starting with a ~M6 normal faulting event, followed ~15 s later by the main event, which included simultaneous normal and right-lateral strike-slip faulting. The aftershock zone extends for 120 km from the south end of the Elsinore fault zone north of the US–Mexico border almost to the northern tip of the Gulf of California. The waveform-relocated aftershocks form two abutting clusters, each about 50 km long, as well as a 10 km north–south aftershock zone just north of the epicenter of the mainshock. Even though the Baja California data are included, the magnitude of completeness and the hypocentral errors increase gradually with distance south of the international border. The spatial distribution of large aftershocks is asymmetric with five M5+ aftershocks located to the south of the mainshock, and only one M5.7 aftershock, but numerous smaller aftershocks to the north. Further, the northwest aftershock cluster exhibits complex faulting on both northwest and northeast planes. Thus, the aftershocks also express a complex pattern of stress release along strike. The overall rate of decay of the aftershocks is similar to the rate of decay of a generic California aftershock sequence. In addition, some triggered seismicity was recorded along the Elsinore and San Jacinto faults to the north, but significant northward migration of aftershocks has not occurred. The synthesis of the El Mayor-Cucapah sequence reveals transtensional regional tectonics, including the westward growth of the Mexicali Valley and the transfer of Pacific–North America plate motion from the Gulf of California in the south into the southernmost San Andreas fault system to the north. We propose that the location of the 2010 El Mayor-Cucapah, as well as the 1992 Landers and 1999 Hector Mine earthquakes, may have been controlled by the bends in the plate boundary.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/24858, title ="Quantifying the forces needed for the rapid change of Pacific plate motion at 6 Ma", author = "Austermann, Jacqueline and Ben-Avraham, Zvi", journal = "Earth and Planetary Science Letters", volume = "307", number = "3-4", pages = "289-297", month = "July", year = "2011", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20110815-111337829", note = "© 2011 Elsevier B.V. \n\nReceived 12 December 2010; revised 18 April 2011; accepted 28 April 2011. Editor: Y. Ricard. Available online 31 May 2011.\n\nWe thank Y. Ricard and three anonymous referees for their\nthoughtful reviews. This work was initiated during Zvi Ben-Avraham's sabbatical at UCLA. We thank the Institute of Geophysics and Planetary Physics and the Department of Earth and Space Sciences at UCLA for their support. We thank G. Iaffaldano for pointing out the link to the Hawaiian-Emperor seamount chain. Funding for Jacqueline Austermann was provided by the Klaus Murmann Fellowship of the Foundation of German Business. California Institute of Technology, Division of Geological and Planetary Sciences, contribution number 10054.\n", revision_no = "18", abstract = "Studies have documented several rapid changes along the Pacific–North American, Pacific–Antarctic and Pacific–Australian plate boundaries in latest Miocene to earliest Pliocene time consistent with a sudden clockwise rotation of Pacific plate velocity relative to hotspots during this period. We test the hypothesis that this change in plate motion was initiated by cessation of subduction along the northern Melanesian arc due to the collision between the arc and the Ontong Java plateau. This hypothesis has long been formulated but never tested quantitatively. We use a geomechanical model of the lithosphere to determine the changes in plate boundary forces that are necessary to obtain the observed change in the Pacific plate motion. Our model results show that the change in motion can be explained by a clockwise rotation of the slab-related (basal-strength) component of plate driving force. The change of slab-related force from a post-6 Ma to a pre-6 Ma setting is perpendicular to the arc and points towards the Australian plate. The force per unit length is in the range of currently accepted values for subduction zones. Since there have been no other relevant changes at subduction zones along the Pacific plate boundary during the latest Miocene, we relate this change in slab-related force to the former southward-dipping Pacific plate slab along the northern Melanesian arc system which is now detached. Our model results suggest that rapid changes in plate motion can be triggered by slab detachment, with consequences for plate boundary processes even at great distances from the event.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/45228, title ="Seismic Calibration Shots Conducted in 2009 in the Imperial Valley, Southern California, for the Salton Seismic Imaging Project (SSIP)", author = "Murphy, Janice and Goldman, Mark", number = "2010-1295", pages = "1-76", month = "January", year = "2011", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140425-103722434", note = "We thank Caltrans (State of California) for allowing us to operate on their land and put seismic recorders in their road right-of-way. We are grateful to the staff at the IRIS-PASSCAL Instrument Center for their help with the instrumentation and software. We especially thank Caltech students Steven Skinner, Yunung Nina Lin, and Wang Yu for their help in the field. They worked tirelessly in temperatures well over 100 degrees and late into the night to the early hours of the morning.", revision_no = "13", abstract = "The Salton Seismic Imaging Project (SSIP) is a large-scale collaborative project with the goal of developing a detailed 3-D structural image of the Salton Trough (including both the Coachella and Imperial Valleys). The image will be used for earthquake hazard analysis, geothermal studies, and studies of plate-boundary transition from an ocean-ocean to a continent-continent plate-boundary.\nAs part of SSIP, a series of calibration shots were detonated in June 2009 in the southern Imperial Valley for four specific reasons: (1) to measure peak particle velocity and acceleration at various distances from the shots, (2) to calibrate the propagation of energy through sediments of the Imperial Valley, (3) to test the effects of seismic energy on buried clay drainage pipes, which are abundant throughout the irrigated parts of the Salton Trough, and (4) to test the ODEX drilling technique, which uses a downhole casing hammer for a tight casing fit.\nCurrently, we are using information obtained from the calibration shots to plan the data collection phase of the SSIP project. We have validated the use of ground-motion tables developed with Los Angeles Region Seismic Experiment (LARSE) data for use in the Imperial Valley and we have demonstrated that seismic energy from shots will not damage the drainage pipes used throughout the Salton Trough for irrigation.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/21567, title ="Submarine landslides along the Malacca Strait-Mergui Basin shelf margin: Insights from sequence-stratigraphic analysis\n\n", author = "Lin, Yu‐nung Nina and Sieh, Kerry", journal = "Journal of Geophysical Research B", volume = "115", pages = "Art. No. B12102", month = "December", year = "2010", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20110104-091738151", note = "© 2011 American Geophysical Union. \n\nReceived 14 October 2009; revised 15 June 2010; accepted 21 July 2010; published 2 December 2010.\n\nWe thank Petroleum Geo‐Services (PGS),\nAsia Pacific center in Singapore for providing the seismic reflection profiles\nused in this study. We also thank Seismic Micro‐Technology (SMT)\nfor providing to Caltech a university grant for the Kingdom Suite software\nused to process these data and generate figures. This project was funded by\na grant from the Earth Observatory of Singapore (EOS grant number\nM61580001) and is EOS Contribution Number 5. Tectonic Observatory\nContribution Number 135.", revision_no = "18", abstract = "The enormously destructive tsunami of December 2004, caused by sudden motion of the Sunda megathrust beneath the Indian Ocean, raised concerns about tectonically induced tsunami worldwide. Submarine landslides may also trigger dangerous tsunami. However, the potential and repeat time for such events is in most places poorly known due to inadequate exploration of the sea floor and age constraints. The high sediment flux and tectonic subsidence rate of the Malacca Strait-Mergui Basin shelf margin NE of northernmost Sumatra provide a favorable environment to generate and preserve submarine landslides. From ten seismic reflection profiles acquired in 2006, we identify three sediment packages that exhibit sliding characteristics such as headscarps, distorted beds and debris-toe structures. We assign lowstand marine isotope stages to the paleo-shoreline indicators observed in the profiles. We then determine the ages of these submarine landslides as 20–30 ka, 342–364 ka and 435–480 ka by the paleo-shoreline indicators that bound the top and bottom of the slide bodies. This sequence-stratigraphic approach shows that these events occurred near times of sea-level lowstands, which implies that a large amount of direct sediment influx during glacial periods is an essential precondition for basin-margin submarine landsliding. Spatiotemporal variations of sediment input due to lobe switching or Asian monsoon intensity changes also control basin-margin instability. Because we are currently at a highstand stage, and sediment flux to the continental margin is relatively small, so the chance of having a repeat submarine landslide and landslide tsunami along this basin-margin is low. \n\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/21174, title ="Abyssal hill deflections at Pacific-Antarctic ridge-transform intersections\n\n", author = "Croon, Marcel B. and Cande, Steven C.", journal = "Geochemistry Geophysics Geosystems", volume = "11", pages = "Art. No. Q11004 ", month = "November", year = "2010", issn = "1525‐2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:20101206-100510765", note = "© 2010 American Geophysical Union.\n\nReceived 25 May 2010; accepted 10 September 2010; published 9 November 2010. \n\n\n\nThis study was made possible through a series of grants\nfrom the NSF Office of Polar Programs, which supported the\nacquisition of geophysical data along transits of the R/VIB\nNathaniel B. Palmer: grants OPP‐0338317, OPP‐0338346,\nOPP‐0126334, and OPP‐0126340. We are grateful to Ifremer\n(Institut français de Recherche pour l’Exploitation de la Mer)\nfor providing multibeam bathymetry data from the PACANTARCTIC\n1 and 2 cruises. We thank the officers, crew, and\nscientific staff of the R/VIB Nathaniel B. Palmer and the many\nstudents who sailed on these cruises. Comments from Jeff Gee,\nDonna Blackman, Roi Granot, and two anonymous reviewers\nhelped us make a number of improvements to the manuscript.\nCaltech contribution 9005.", revision_no = "15", abstract = "Nearly complete coverage of shipboard multibeam bathymetry data at the right-stepping Menard and Pitman Fracture Zones allowed us to map abyssal hill deviations along their traces. In this study we distinguish between (1) J-shaped curvatures at their origin, where modeling is addressing primary volcanism and faulting following a curved zone, and (2) straight abyssal hills getting bent in anti-J-shaped curvatures, in response to increased coupling across the transform fault, after they were formed. We compared the mapped abyssal hill deflections to a detailed plate motion model for the Pacific-Antarctic Ridge to test how abyssal hill curvature correlates to changes in plate motion direction, which lead to periods of transtension or transpression. This test was based on the number and size of the abyssal hill deflections. The observations show a high abundance of J-shaped abyssal hills during periods of significant clockwise change in plate motion direction, which leads to transtension. The tip of the ridge axis can deflect up to 60° into the transform fault in response to changes in the stress field at ridge-transform intersections. This is observed, in particular, at the Pitman Fracture Zone, where there has been a ∼15° clockwise rotation of the spreading direction azimuth during the last 9 Myr. In addition, we observed anti-J-shaped curvatures at Menard, Pitman, and Heirtzler Fracture Zones during periods of transpression when increased coupling across an oceanic transform fault is partially accommodated by distributed strike-slip deformation rather than solely by discontinuous displacement at the transform fault. Anti-J-shaped deflections typically develop in seafloor less than 2 Myr old when the oceanic lithosphere is thin. \n\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/19709, title ="Postspreading rifting in the Adare Basin, Antarctica: Regional tectonic consequences", author = "Granot, R. and Cande, S. C.", journal = "Geochemistry, Geophysics, Geosystems", volume = "11", pages = "Art. No. Q08005 ", month = "August", year = "2010", doi = "10.1029/2010GC003105 ", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:20100830-113018904", note = "© 2010 American Geophysical Union.\n\nReceived 26 February 2010; accepted 6 May 2010; published 4 August 2010. \nWe would like to thank Captain M. Watson, the crew,\nand the Raytheon staff of the R/VIB Nathaniel B. Palmer for\ntheir dedicated work during cruise NBP0701. Also, we thank\nDietmar Müller and Sean Gulick for their helpful reviews;\nNeal Driscoll, Donna Blackman, and Jeff Gee for helpful discussions;\nPaul Henkart for the continuous help with SIOSEIS;\nand Chris Sorlein for introducing us to SPW software. Detlef\nDamaske is thanked for making the aeromagnetic data available\nfor us. Interpretation of the seismic profiles was done with\nKingdom Suite, a contribution of Seismic Micro‐Technology.\nThis project was funded by NSF grant OPP04‐40959 (SIO)\nand OPP04‐40923 (Caltech).", revision_no = "15", abstract = "Extension during the middle Cenozoic (43–26 Ma) in the north end of the West Antarctic rift system (WARS) is well constrained by seafloor magnetic anomalies formed at the extinct Adare spreading axis. Kinematic solutions for this time interval suggest a southward decrease in relative motion between East and West Antarctica. Here we present multichannel seismic reflection and seafloor mapping data acquired within and near the Adare Basin on a recent geophysical cruise. We have traced the ANTOSTRAT seismic stratigraphic framework from the northwest Ross Sea into the Adare Basin, verified and tied to DSDP drill sites 273 and 274. Our results reveal three distinct periods of tectonic activity. An early localized deformational event took place close to the cessation of seafloor spreading in the Adare Basin (~24 Ma). It reactivated a few normal faults and initiated the formation of the Adare Trough. A prominent pulse of rifting in the early Miocene (~17 Ma) resulted in normal faulting that initiated tilted blocks. The overall trend of structures was NE–SW, linking the event with the activity outside the basin. It resulted in major uplift of the Adare Trough and marks the last extensional phase of the Adare Basin. Recent volcanic vents (Pliocene to present day) tend to align with the early Miocene structures and the on-land Hallett volcanic province. This latest phase of tectonic activity also involves near-vertical normal faulting (still active in places) with negligible horizontal consequences. The early Miocene extensional event found within the Adare Basin does not require a change in the relative motion between East and West Antarctica. However, the lack of subsequent rifting within the Adare Basin coupled with the formation of the Terror Rift and an on-land and subice extension within the WARS require a pronounced change in the kinematics of the rift. These observations indicate that extension increased southward, therefore suggesting that a major change in relative plate motion took place in the middle Miocene. The late Miocene pole of rotation might have been located north of the Adare Basin, with opposite opening sign compared to the Eocene-Oligocene pole. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/16246, title ="Pulling plates apart", author = "Stock, Joann M.", journal = "Nature Geoscience", volume = "2", number = "8", pages = "541-542", month = "August", year = "2009", issn = "1752-0894", url = "https://resolver.caltech.edu/CaltechAUTHORS:20091012-125444405", note = "© 2009 Nature Publishing Group.", revision_no = "12", abstract = "The Salton Sea is located in a sedimentary basin at the southern termination of the San Andreas fault. High-resolution seismic data indicate that the basin formed and grew by active subsidence at its southern end.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/15218, title ="Slowing of India's convergence with Eurasia since 20 Ma and its implications for Tibetan mantle dynamics", author = "Molnar, Peter and Stock, Joann M.", journal = "Tectonics", volume = "28", pages = "TC3001", month = "May", year = "2009", issn = "0278-7407", url = "https://resolver.caltech.edu/CaltechAUTHORS:20090821-081957305", note = "© 2009 American Geophysical Union.\nReceived 6 February 2008; accepted 10 March 2009; published 16 May 2009. \n\nOne of us was justifiably provoked by\nMarin Clark’s question in 2003, \"Wouldn’t you expect a change in plate\nmotions at 8 Ma\"? C. DeMets both offered useful suggestions for\nimproving the manuscript and supplied us with preprints in advance of\npublication. This research was supported in part by the National Science\nFoundation under grants EAR-0440004, EAR 0507330, EAR 0636092, and\nOPP-0338317. Figures 2, 4, and 5 were made using Generic Mapping Tools\n(GMT) software.", revision_no = "15", abstract = "Reconstructions of the relative positions of the India and Eurasia plates, using recently revised histories of movement between India and Somalia and between North America and Eurasia and of the opening of the East African Rift, show that India's convergence rate with Eurasia slowed by more than 40% between 20 and 10 Ma. Much evidence suggests that beginning in that interval, the Tibetan Plateau grew outward rapidly and that radially oriented compressive strain in the area surrounding Tibet increased. An abrupt increase in the mean elevation of the plateau provides a simple explanation for all of these changes. Elementary calculations show that removal of mantle lithosphere from beneath Tibet, or from just part of it, would lead to both a modest increase in the mean elevation of the plateau of ~1 km and a substantial change in the balance of forces per unit length applied to the India and Eurasia plates.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/12557, title ="Isotope geochemistry and petrogenesis of peralkaline Middle Miocene ignimbrites from central Sonora: relationship with continental break-up and the birth of the Gulf of California", author = "Vidal Solano, Jesús R. and Lapierre, Henriette", journal = "Bulletin de la Société Géologique de France", volume = "179", number = "5", pages = "453-464", month = "September", year = "2008", issn = "0037-9409", url = "https://resolver.caltech.edu/CaltechAUTHORS:VIDbsgf08", note = "© 2008 Société Géologique de France. \n\nManuscript received 20 February 2007; accepted after revision 11 September 2007. \n\nThis study is part of the Ph.D. thesis of the senior author at the Université Paul Cézanne (Aix-Marseille 3). This work was funded by CONACYT and SFERE (129313/168910) scholarship grant. Sampling and mapping were carried out from 1999 to 2005 with the financial support of the Departamento de Geología de la Universidad de Sonora. Thanks to M.O. Trensz (ICP-AES analyses, CEREGE) to J.-C. Girard (thin-section preparation) and C. Merlet (electron microprobe, ISTEEM Montpellier). ENS Lyon supported Pb isotope facilities. This work also benefited from a 6 months post-doctoral fellowship at Seismo Lab in Caltech, supported by the US National Science Foundation grant EAR-0336961. Reviews by Christian Picard and Marc Tardy help to improve the manuscript. \n\n[H.L.] - Décédée en Janvier 2006.", revision_no = "17", abstract = "Middle Miocene peralkaline ignimbrites constitute a specific geodynamic marker of the early stage of opening of the Gulf of California, preserved either in central Sonora or the Puertecitos area, in Baja California. Very uniform ages (12-12.5 Ma) obtained on these rocks show that this volcanic episode corresponds to a specific stage in the tectonic evolution of the proto-gulf area. Field observations and slightly different Sr and Nd isotopic signatures support eruptions from several small volume magma batches rather than from a large-volume caldera forming event. Isotopic ratios help to constrain the petrogenesis of the peralkaline liquids by fractional crystallization of transitional basalts in a shallow reservoir, with slight contamination by Precambrian upper crustal material. Less differentiated glomeroporphyritic icelandites erupted at about 11 Ma, mark an increase in the magma production rate and highlight an easier access to the surface, illustrating an advanced stage in the weakening of the continental crust. The tilting of the Middle Tertiary sequences results from a major change in the tectonic regime, from E-W extension giving rise to N-S grabens, to NNW-SSE strike-slip motion that can be related to the transfer of Baja California from North America to the Pacific plate. The location of peralkaline volcanism coincides with the southern edge of the Precambrian crust and the southernmost extension of the California slab window at 12.5 Ma.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/11235, title ="Revised Pacific-Antarctic plate motions and geophysics of the Menard Fracture Zone", author = "Croon, Marcel B. and Cande, Steven C.", journal = "Geochemistry, Geophysics, Geosystems", volume = "9", number = "7", pages = "2008GC002019", month = "July", year = "2008", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:CROggg08", note = "Copyright 2008 by the American Geophysical Union. \n\nReceived 5 March 2008; accepted 15 May 2008; published 1 July 2008. \n\nThis study was made possible through a series of grants from the NSF-Office of Polar Programs supporting the acquisition of geophysical data along transits of the R/VIB Nathaniel B. Palmer: grants OPP-0338317, OPP-0338346, OPP-0126334, and OPP-0126340. We thank the officers, crew, and scientific staff of the R/VIB Nathaniel B. Palmer and the many students who sailed on these cruises. Caltech contribution 9005.", revision_no = "14", abstract = "A reconnaissance survey of multibeam bathymetry and magnetic anomaly data of the Menard Fracture Zone allows for significant refinement of plate motion history of the South Pacific over the last 44 million years. The right-stepping Menard Fracture Zone developed at the northern end of the Pacific-Antarctic Ridge within a propagating rift system that generated the Hudson microplate and formed the conjugate Henry and Hudson Troughs as a response to a major plate reorganization ∼45 million years ago. Two splays, originally about 30 to 35 km apart, narrowed gradually to a corridor of 5 to 10 km width, while lineation azimuths experienced an 8° counterclockwise reorientation owing to changes in spreading direction between chrons C13o and C6C (33 to 24 million years ago). We use the improved Pacific-Antarctic plate motions to analyze the development of the southwest end of the Pacific-Antarctic Ridge. Owing to a 45° counterclockwise reorientation between chrons C27 and C20 (61 to 44 million years ago) this section of the ridge became a long transform fault connected to the Macquarie Triple Junction. Following a clockwise change starting around chron C13o (33 million years ago), the transform fault opened. A counterclockwise change starting around chron C10y (28 millions years ago) again led to a long transform fault between chrons C6C and C5y (24 to 10 million years ago). A second period of clockwise reorientation starting around chron C5y (10 million years ago) put the transform fault into extension, forming an array of 15 en echelon transform faults and short linking spreading centers.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/34574, title ="Vertical tectonics of the High Plateau region, Manihiki Plateau, Western Pacific, from seismic stratigraphy", author = "Ai, Huirong-Anita and Stock, Joann M.", journal = "Marine Geophysical Research", volume = "29", number = "1", pages = "13-26", month = "January", year = "2008", doi = "10.1007/s11001-008-9042-0", issn = "0025-3235", url = "https://resolver.caltech.edu/CaltechAUTHORS:20121001-090154547", note = "© 2008 The Author(s). Received: 2 May 2006; Accepted: 19 January 2008. This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. We thank Patricia Persaud for her insightful\ndiscussion and numerous suggestions. We also thank graduate and undergraduate students from Caltech and UC Santa Barbara for their assistance on KIWI 12. Research supported by University of\nCalifornia San Diego, Scripps Institution of Oceanography, UC Santa Barbara, and Caltech. Nathaniel B. Palmer multibeam data collection was supported by NSF OPP-0126334. Contribution 8945, Division of Geological and Planetary Sciences, California Institute of Technology.\nContribution of the Institute for Crustal Studies, University of California, Santa Barbara, number 0810.", revision_no = "19", abstract = "The Manihiki Plateau is an elevated oceanic volcanic plateau that was formed mostly in Early Cretaceous time by hotspot activity. We analyze new seismic reflection data acquired on cruise KIWI 12 over the High Plateau region in the southeast of the plateau, to look for direct evidence of the location of the heat source and the timing of uplift, subsidence and faulting. These data are correlated with previous seismic reflection lines from cruise CATO 3, and with the results at DSDP Site 317 at the northern edge of the High Plateau. Seven key reflectors are identified from the seismic reflection profiles and the resulting isopach maps show local variations in thickness in the southeastern part of the High Plateau, suggesting a subsidence (cooling) event in this region during Late Cretaceous and up to Early Eocene time. We model this as a hotspot, active and centered on the High Plateau area during Early Cretaceous time in a near-ridge environment. The basement and Early Cretaceous volcaniclastic layers were formed by subaerial and shallow-water eruption due to the volcanic activity. After that, the plateau experienced erosion. The cessation of hotspot activity and subsequent heat loss by Late Cretaceous time caused the plateau to subside rapidly. The eastern and southern portions of the High Plateau were rifted away following the cessation of hot spot activity. As the southeastern portion of the High Plateau was originally higher and above the calcium carbonate compensation depth, it accumulated more sediments than the surrounding plateau regions. Apparently coeval with the rapid subsidence of the plateau are normal faults found at the SE edge of the plateau. Since Early Eocene time, the plateau subsided to its present depth without significant deformation. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/86100, title ="COBBOOM: The Continental Breakkup and Birth of Oceans Mission", author = "Sawyer, Dale S. and Coffin, Millard F.", journal = "Scientific Drilling", volume = "5", pages = "13-25", month = "September", year = "2007", doi = "10.2204/iodp.sd.5.02.2007", issn = "1816-3459", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180427-155654058", note = "© Author(s) 2007. This work is distributed under the Creative Commons Attribution 3.0 License. \n\nThe authors appreciate input to this paper by participants in the IODP Workshop on Continental Breakup and Sedimentary Basin Formation as well as contributors who did not attend the workshop. We thank the IODP for providing the principal funding for the workshop held in Pontresina, Switzerland on 15–18 September 2006. We thank InterMARGINS for making it possible for scientists from non-IODP member countries to participate in the workshop. Gianreto Manatschal handled the logistics of the workshop and led an incredible field trip to a rifted margin crust and exhumed upper mantle in the Alps. Finally, we acknowledge the essential contributions of Kelly Kryc of IODP-MI who organized the workshop.", revision_no = "9", abstract = "The rupture of continents and creation of new oceans is a fundamental yet primitively understood aspect of the plate tectonic cycle. Building upon past achievements by ocean drilling and geophysical and geologic studies, we propose “The Continental Breakup and Birth of Oceans Mission (COBBOOM)” as the next major phase of discovery, for which sampling by drilling will be essential. \n\nIn September 2006, fifty-one scientists from six continents gathered in Pontresina, Switzerland to discuss current knowledge of continental breakup and sedimentary basin formation and how the Integrated Ocean Drilling Program (IODP) can deepen that knowledge (Coffin et al., 2006). Workshop participants discussed a global array of rifted margins (Fig. 1), formulated the critical problems to be addressed by future drilling and related investigations, and identified key rift systems poised for IODP investigations.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/106880, title ="COBBOOM: The Continental Breakup and Birth of Oceans Mission", author = "Sawyer, Dale S. and Coffin, Millard F.", journal = "Scientific Drilling", volume = "5", pages = "13-25", month = "September", year = "2007", doi = "10.2204/iodp.sd.5.02.2007", issn = "1816-3459", url = "https://resolver.caltech.edu/CaltechAUTHORS:20201202-151324692", note = "© Author(s) 2007. This work is distributed under the Creative Commons Attribution 3.0 License. \n\nThe authors appreciate input to this paper by participants\nin the IODP Workshop on Continental Breakup and Sedimentary Basin Formation as well as contributors who did not attend the workshop. We thank the IODP for providing the principal funding for the workshop held in Pontresina, Switzerland on 15–18 September 2006. We thank InterMARGINS for making it possible for scientists from non-IODP member countries to participate in the workshop. Gianreto Manatschal handled the logistics of the workshop and led an incredible field trip to a rifted margin crust and exhumed upper mantle in the Alps. Finally, we acknowledge the essential contributions of\nKelly Kryc of IODP-MI who organized the workshop.", revision_no = "14", abstract = "The rupture of continents and creation of new oceans is a\nfundamental yet primitively understood aspect of the plate\ntectonic cycle. Building upon past achievements by ocean\ndrilling and geophysical and geologic studies, we propose\n“The Continental Breakup and Birth of Oceans Mission\n(COBBOOM)” as the next major phase of discovery, for\nwhich sampling by drilling will be essential.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/17547, title ="A geodetic study of the 2003 January 22 Tecomán, Colima, Mexico earthquake", author = "Schmitt, Stuart V. and DeMets, Charles", journal = "Geophysical Journal International", volume = "169", number = "2", pages = "389-406", month = "May", year = "2007", doi = "10.1111/j.1365-246X.2006.03322.x ", issn = "0956-540X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20100222-095232667", note = "© 2007 The Authors. Journal compilation © 2007 RAS.\n\nAccepted 2006 December 5; received 2006 December 4; in original form 2006 February 8.\n\nNumerous individuals assisted us in our field efforts. We thank Bill Unger of the University of Wisconsin Department of Geology and Geophysics for the long hours he has dedicated to this project for the past decade. We also thank Bill and Ana Douglass of Ajijic for their hospitality and field assistance, the Universidad de Guadalajara for access to a field vehicle and GPS equipment, Antonio Hernandez of INEGI for access to data from their GPS sites and Proteccion Civil of the state of Jalisco for logistical support. Support from NSF grants EAR-9909377 and EAR-9909321 made this work possible.", revision_no = "21", abstract = "We use coseismic displacements and aftershock information from Global Positioning System (GPS) measurements at 27 sites in western Mexico and a 12-station local seismic network to determine the characteristics of the 2003 January 22 M_w = 7.2 subduction thrust earthquake near Tecomán, Colima, Mexico. Estimates of the earthquake moment, slip direction and best-fitting slip distribution are derived by optimizing the fit to the GPS displacements for a 3-D finite element mesh that simulates the study area. The calculated moment release is 9.1 × 10^(19) N m (M_w = 7.2) , with maximum slip of 2 m at a depth of 24 km and a maximum rupture depth of 35–40 km. The inversion indicates that coseismic rupture extended downdip from depths of 9 to 40 km along a 80 km along-strike region that is bounded by the edges of the Manzanillo Trough. The optimal solution is robust with respect to plausible changes in the subduction interface geometry and differing subsets of the data. A comparison of the cumulative post-seismic slip that can be inferred separately from earthquake aftershocks and GPS measurements within a year of the earthquake indicates that 95 per cent or more of the post-seismic deformation was aseismic. Near-term post-seismic measurements indicate that slip propagated downdip to areas of the subduction interface beneath the coastline within days following the earthquake, as also occurred after the nearby M_w = 8.0 Colima-Jalisco subduction earthquake in 1995. The similar behaviours and locations of the 1995/2003 earthquake sequence to two earthquakes in June of 1932 suggests that thrust earthquakes along the subduction interface northwest of the Manzanillo Trough may trigger earthquakes in the vicinity of the Manzanillo Trough; however, our modelling of Coulomb stress changes caused by the 1995 earthquake indicate that it induced only modest unclamping of the subduction interface in the vicinity of the Tecomán rupture. In addition, GPS measurements indicate that elastic shortening characterized areas onshore from the Tecomán rupture from mid-1997 up until the time of the rupture, consistent with progressively stronger clamping of the subduction interface during this period. This precludes any obvious triggering relationship with the 1995 earthquake. The apparent coincidence of the edge of both the 1932 and 1995/2003 rupture sequences with the edge of the Manzanillo Trough may indicate that the trough is a mechanical barrier to along-strike rupture propagation. This implies a limit to the area of potential slip and hence rupture magnitude during future large earthquakes in this region.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/34579, title ="History of the Cretaceous Osbourn spreading center", author = "Downey, Nathan J. and Stock, Joann M.", journal = "Journal of Geophysical Research B", volume = "112", number = "B4", pages = "Art. No. B04102", month = "April", year = "2007", doi = "10.1029/2006JB004550", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20121001-094812502", note = "© 2007 by the American Geophysical Union. Received 7 June 2006; revised 5 October 2006; accepted 1 November 2006; published 6 April 2007. The Palmer cruises were supported by NSF grant OPP-0126334. Subsequent data analysis was supported by NSF grant\nOPP-0338317. We thank the Captain and crew of both the R/VIB Nathaniel B. Palmer and the R/V Kilo Moana. Brian Taylor provided us the opportunity to participate in, and use data from, cruise KM0413. We also thank Steve Miller for permission to use the COOK20 data. We thank Brian Taylor and an anonymous reviewer for insightful reviews that greatly improved this paper. California Institute of Technology Division of Geological and Planetary Sciences, contribution number 9148.", revision_no = "19", abstract = "The Osbourn Trough is a fossil spreading center that rifted apart the Manihiki and Hikurangi Plateaus during Cretaceous time. Previous models of the Osbourn spreading center are based on data collected near the trough axis, and therefore only constrain the history of the Osbourn spreading center during the last few Ma of spreading. Our data set includes multibeam data collected northward to the Manihiki Plateau, allowing us to examine seafloor morphology created during the entire active period of the Osbourn spreading center, as well as several additional multibeam data sets that provide the opportunity to examine the relationship between the Osbourn paleospreading center and the Cretaceous Pacific-Phoenix ridge. The axial gravity of the trough is similar to the gravity found at other extinct slow-intermediate spreading rate ridges. Magnetic field measurements indicate that spreading at the trough ceased during Chron C34. Abyssal-hill trends indicate that spreading during the early history of the Osbourn spreading center occurred at 15°–20°. The east-west component of this spreading explains the modern east-west offset of the Manihiki and Hikurangi Plateaus. Spreading rotated to 2°–5° prior to extinction. Abyssal-hill RMS amplitudes show that a decrease in spreading rate, from >7 cm/yr to 2–6 cm/yr full-spreading rate, occurred ∼2–6 Ma prior to ridge extinction. Our data analysis is unable to determine the exact spreading rate of the Osbourn spreading center prior to the slowing event. The temporal constraints provided by our data show that the Osbourn spreading center ceased spreading prior to 87 Ma or 93 Ma, depending on whether the Manihiki and Hikurangi Plateaus rifted at 115 Ma or 121 Ma. Our model resolves the conflict between regional models of Osbourn spreading with models based on trough characteristics by showing that spreading at the Osbourn spreading center was decoupled from Pacific-Phoenix spreading. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/45879, title ="Extension in the western Ross Sea region-links between Adare Basin and Victoria Land Basin", author = "Davey, F. J. and Cande, S. C.", journal = "Geophysical Research Letters", volume = "33", number = "20", pages = "Art. No. L20315", month = "October", year = "2006", doi = "10.1029/2006GL027383", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140522-084410391", note = "© 2006 American Geophysical Union. Manuscript Accepted: 19 Sep 2006. Manuscript Received: 24 Jul 2006. Article first published online: 27 Oct 2006. We greatly appreciated a review of the manuscript by an anonymous reviewer. We acknowledge the support of the Captain and crew of R/V NB Palmer during the acquisition of data over southern Adare Basin. The research was supported by NSF grants\nOPP-0338346 (S Cande) and OPP-0338317 (J. Stock), by the NZ\nFoundation for Research, Science and Technology and the NZ GSF (F. Davey).", revision_no = "11", abstract = "Spreading in the Adare Basin off north-western Ross Sea (43–26 Ma) and extension in the Victoria Land Basin (VLB, > 36 Ma) are used to constrain the pole of rotation for the Adare Basin, providing a rifting model for the region for the past 45 Ma. The offset from Northern Basin to VLB at about 74°S coincides with the linear Polar-3 magnetic anomaly, inferred to be caused by a major 48 - 34 Ma igneous intrusion. The style of extension apparently changed at about 34 Ma, with the end of intrusion at the Polar-3 anomaly, a change from highly asymmetric extension in Adare Basin, and the onset of major subsidence on the flanks of VLB. Ductile lower crustal and lithospheric flow is proposed as the cause of the inferred thick crust underlying southern Adare Basin, and a result of the constraining of extension to the adjacent contiguous Northern Basin.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44990, title ="The Hawaiian-Emperor Bend: Older than expected", author = "Stock, Joann M.", journal = "Science", volume = "313", number = "5791", pages = "1250-1251", month = "September", year = "2006", doi = "10.1126/science.1131789 ", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140416-152556111", note = "© 2006 American Association for the Advancement of Science.", revision_no = "11", abstract = "The kink in the Hawaiian-Emperor seamount chain in the Pacific Ocean was initiated ~50 million years ago, at a time when major plate motion changes occurred.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/50495, title ="Constraints on the timing of extension in the Northern Basin, Ross Sea", author = "Cande, Steven C. and Stock, Joann M.", pages = "319-326", month = "January", year = "2006", isbn = "978-3-540-30673-3", url = "https://resolver.caltech.edu/CaltechAUTHORS:20141017-125224927", note = "© 2006 Springer-Verlag Berlin Heidelberg\n\nWe thank the captains, officers, crew and scientific staff\nof the R/VIB \"Nathaniel Palmer\" for their dedicated Efforts\nDr. Takemi Ishihara generously provided us with\nseismic reflection and magnetics data from the RV\n\"Hakurei Maru\". Two anonymous reviewers provided\nhelpful comments This work was supported by NSF grants\nOPP-03-38346 (Cande) and OPP-03-38317 (Stock).", revision_no = "13", abstract = "Recent kinematic constraints for the region north of the western Ross Sea suggest that there was approximately 150 km of seafloor spreading in the Adare Basin, northeast of Cape Adare, between Chrons 20 and 8 (43 to 26 Ma). This kinematic history has important implications since the 150 km of extension in the Adare Basin occurred immediately north along strike from the Northern Basin of the Ross Sea, whose extensional history is not well known. This paper examines the transition from the structures in the Adare Basin to the structures of the Northern Basin and speculates on the manner in which the extension was accommodated in the Ross Sea. Magnetic anomaly data in the Adare Basin document a sequence of anomalies 18 to 12 formed during a period of very slow spreading. The easternmost part of this sequence, anomalies 16 to 18, coalesces into a single positive anomaly near 72° S, forming a distinct anomaly that can be traced southward from the Adare Basin across the continental margin and down the east side of the Northern Basin to a latitude of roughly 73° S. This observation has important implications for the tectonic history of the Ross Sea since it suggests that most of the extension in the Adare Basin continued into the Northern Basin. This, in turn, suggests that the Northern Basin was formed by a combination of crustal thinning and massive, narrowly focused intrusions.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/1107, title ="Crustal structure and rift flank uplift of the Adare Trough, Antarctica", author = "Müller, R. Dietmar and Cande, Steven C.", journal = "Geochemistry, Geophysics, Geosystems", volume = "6", number = "11", pages = "2005GC001027", month = "November", year = "2005", issn = "1525-2027", url = "https://resolver.caltech.edu/CaltechAUTHORS:MULggg05", note = "Copyright 2005 by the American Geophysical Union. \n\nReceived: 24 May 2005; Revised: 23 August 2005; Accepted: 27 September 2005; Published: 23 November 2005. \n\nThis work was supported by National Science Foundation grants NSF OPP 0126334 (to Stock) and OPP-01-26340 (to Cande) and by an Australian Research Council IREX grant (to Müller). We thank Bernhard Steinberger for providing outputs from his mantle convection model published in Steinberger et al. [2004]. Two anonymous reviews improved the quality of the paper substantially.", revision_no = "8", abstract = "The Adare Trough, located 100 km northeast of Cape Adare, Antarctica, represents the extinct third arm of a Tertiary spreading ridge between East and West Antarctica. It is characterized by pronounced asymmetric rift flanks elevated up to over 2 km above the trough's basement, accompanied by a large positive mantle Bouguer anomaly. On the basis of recently acquired seismic reflection and ship gravity data, we invert mantle Bouguer anomalies from the Adare Trough and obtain an unexpectedly large oceanic crustal thickness maximum of 9–10.5 km underneath the extinct ridge. A regional positive residual basement depth anomaly between 1 and 2.5 km in amplitude characterizes ocean crust from offshore Victoria Land to the Balleny Islands and north of Iselin Bank. The observations and models indicate that the mid/late Tertiary episode of slow spreading between East and West Antarctica was associated with a mantle thermal anomaly. The increasing crustal thickness toward the extinct ridge indicates that this thermal mantle anomaly may have increased in amplitude through time during the Adare spreading episode. This scenario is supported by a mantle convection model, which indicates the formation and strengthening of a major regional negative upper mantle density anomaly in the southwest Pacific in the last 50 million years. The total amount of post-26 Ma extension associated with Adare Trough normal faulting was about 7.5 km, in anomalously thick oceanic crust with a lithospheric effective elastic thickness (EET) between 3.5 and 5 km. This corresponds to an age between 3 and 5 million years based on a thermal boundary layer model and supports a scenario in which the Adare Trough formed soon after spreading between East and West Antarctica ceased, confined to relatively weak lithosphere with anomalously thick oceanic crust. There is little evidence for major subsequent structural activity in the Adare trough area from the available seismic data, indicating that this part of the West Antarctic Rift system became largely inactive in the early Miocene, with the exception of minor structural reactivation which is visible in the seismic data as offsets up to end of the early Pliocene.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/45876, title ="Mapping variations in weight percent silica measured from multispectral thermal infrared imagery—Examples from the Hiller Mountains, Nevada, USA and Tres Virgenes-La Reforma, Baja California Sur, Mexico", author = "Hook, Simon J. and Dmochowski, Jane E.", journal = "Remote Sensing of Environment", volume = "95", number = "3", pages = "273-289", month = "April", year = "2005", doi = "10.1016/j.rse.2004.11.020", issn = "0034-4257", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140522-071230681", note = "© 2005 Elsevier Inc. Received 25 February 2004; received in revised form 18 November 2004; accepted 19 November 2004\nAbstract. The research described in this paper was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration as part of the Earth Observing System Mission to Planet Earth Program. The work by Jane Dmochowski was funded by a NASA Earth System Science\nFellowship Grant NGT5-30393. Numerous people have contributed to this work. In particular we would like to thank Ron Alley at JPL for help with atmospherically correcting the data and Mike Rymer and Kevin Mullins both at the USGS for reviewing the manuscript. Reference herein to any specific commercial product, process, or service by trade names, trademark, manufacturer or otherwise does not imply endorsement by the United States or the Jet Propulsion Laboratory, California Institute of Technology. Contribution number 9111, Division of Geological and Planetary Sciences, California Institute of Technology.", revision_no = "12", abstract = "Remotely sensed multispectral thermal infrared (8–13 μm) images are increasingly being used to map variations in surface silicate mineralogy. These studies utilize the shift to longer wavelengths in the main spectral feature in minerals in this wavelength region (reststrahlen band) as the mineralogy changes from felsic to mafic. An approach is described for determining the amount of this shift and then using the shift with a reference curve, derived from laboratory data, to remotely determine the weight percent SiO_2 of the surface. The approach has broad applicability to many study areas and can also be fine-tuned to give greater accuracy in a particular study area if field samples are available. The approach was assessed using airborne multispectral thermal infrared images from the Hiller Mountains, Nevada, USA and the Tres Virgenes-La Reforma, Baja California Sur, Mexico. Results indicate the general approach slightly overestimates the weight percent SiO_2 of low silica rocks (e.g. basalt) and underestimates the weight percent SiO_2 of high silica rocks (e.g. granite). Fine tuning the general approach with measurements from field samples provided good results for both areas with errors in the recovered weight percent SiO_2 of a few percent. The map units identified by these techniques and traditional mapping at the Hiller Mountains demonstrate the continuity of the crystalline rocks from the Hiller Mountains southward to the White Hills supporting the idea that these ranges represent an essentially continuous footwall block below a regional detachment. Results from the Baja California data verify the most recent volcanism to be basaltic–andesite", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44970, title ="Pacific-Antarctic-Australia motion and the formation of the Macquarie Plate", author = "Cande, Steven C. and Stock, Joann M.", journal = "Geophysical Journal International", volume = "157", number = "1", pages = "399-414", month = "April", year = "2004", doi = "10.1111/j.1365-246X.2004.02224.x ", issn = "0956-540X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140416-090150847", note = "© 2004 RAS.\n\nAccepted 2003 December 15. Received 2003 November 25; in original form 2002 November 25.\n\nThis study was made possible through grants from the NSF-Office\nof Polar Programs supporting the acquisition of underway geophysical\ndata on long transits of the R/VIB Nathaniel B. Palmer. We\nthank the officers, crew and scientific staff of the R/VIB Nathaniel\nB. Palmer and the many graduate students and other scientists, especially\nStan Jacobs, who have contributed to this programme. M.\nCoffin, C. DeMets and R. Gordon gave helpful reviews. GMT software\nwas used to produce the figures (Wessel & Smith 1991). This\nprogramme was supported by NSF grants OPP-0126340 (UCSD)\nand OPP-0126334 (Caltech). California Institute of Technology Division\nof Geological and Planetary Sciences contribution number\n9032.", revision_no = "11", abstract = "Magnetic anomaly and fracture zone data on the Southeast Indian Ridge (SEIR) are analysed in order to constrain the kinematic history of the Macquarie Plate, the region of the Australian Plate roughly east of 145°E and south of 52°S. Finite rotations for Australia–Antarctic motion are determined for nine chrons (2Ay, 3Ay, 5o, 6o, 8o, 10o, 12o, 13o and 17o) using data limited to the region between 88°E and 139°E. These rotations are used to generate synthetic flowlines which are compared with the observed trends of the easternmost fracture zones on the SEIR. An analysis of the synthetic flowlines shows that the Macquarie Plate region has behaved as an independent rigid plate for roughly the last 6 Myr. Finite rotations for Macquarie–Antarctic motion are determined for chrons 2Ay and 3Ay. These rotations are summed with Australia–Antarctic rotations to determine Macquarie–Australia rotations. We find that the best-fit Macquarie–Australia rotation poles lie within the zone of diffuse intraplate seismicity in the South Tasman Sea separating the Macquarie Plate from the main part of the Australian Plate. Motion of the Macquarie Plate relative to the Pacific Plate for chrons 2Ay and 3Ay is determined by summing Macquarie–Antarctic and Antarctic–Pacific rotations. The Pacific–Macquarie rotations predict a smaller rate of convergence perpendicular to the Hjort Trench than the Pacific–Australia rotations. The onset of the deformation of the South Tasman Sea and the development of the Macquarie Plate appears to have been triggered by the subduction of young, buoyant oceanic crust near the Hjort Trench and coincided with a clockwise change in Pacific–Australia motion around 6 Ma. The revised Pacific–Australia rotations also have implications for the tectonics of the Alpine Fault Zone of New Zealand. We find that changes in relative displacement along the Alpine Fault have been small over the last 20 Myr. The average rate of convergence over the last 6 Myr is about 40 per cent smaller than in previous models.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/45231, title ="Cenozoic Reconstructions of the Australia-New Zealand-South Pacific Sector of Antarctica", author = "Cande, Steven C. and Stock, Joann M.", number = "151", pages = "5-17", month = "January", year = "2004", doi = "10.1029/151GM02", isbn = "9780875904160", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140425-125510082", note = "© 2004 American Geophysical Union.\nWe thank Rob Larter and Carmen Gaina for\ntheir helpful reviews and Neville Exon for hi editorial suggestions.\nGMT software was used to produce the figures [Wessel and Smith, 1991]. This research was supported by NSF grant OPP-0126340\n(UCSD) and OPP-0126334 (Caltech). California Institute of\nTechnology Division of Geological and Planetary Science contribution\nnumber 8956.", revision_no = "14", abstract = "Reconstructions are presented documenting the relative motion of the Australia.\nAntarctic and Pacific plates since Chron 27 (61.1 Ma). In addition to the motion of\nthe major plates, the reconstructions show the relative motion between East and\nWest Antarctica and the continental fragments that make up the South Tasman\nRise. Recent observations that are used in making these reconstructions include the\nmapping of seafloor spreading magnetic anomalies in the Adare basin, northeast of\nCape Adare, which recorded roughly 150 km of opening between East and West\nAntarctica between Chrons 20 (43.8 Ma) and 8 (26.6 Ma). In addition, magnetic\nand bathymetric observations from the lselin Rift, northeast of the Iselin Bank, and\nfrom the Emerald Fracture Zone, along the western boundary of Pacific-Antarctic\nspreading, document the rotation of the Iselin Bank between Chrons 27 and 24\n(53.3 Ma). Our reconstructions indicate that there was a total of about 200 km of\nseparation between East and West Antarctica in the northern Ross Sea region in the\nCenozoic. These reconstructions document the development of a deep-water\npassageway between Australia and Antarctica as the South Tasman Rise clears the\nfinal piece of the Antarctic continental margin around Chron 13 (33.5 Ma).", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/20980, title ="Cenozoic evolution of Neotethys and implications for the causes of plate motions", author = "McQuarrie, N. and Stock, J. M.", journal = "Geophysical Research Letters", volume = "30", number = "20", pages = "Art. No. 2036", month = "October", year = "2003", doi = "10.1029/2003GL017992 ", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20101123-103005860", note = "© 2003 American Geophysical Union.\n\nReceived 17 June 2003; revised 26 August 2003; accepted 2 September 2003; published 21 October 2003.\n\nWe thank Peter Molnar and Dietmar Mueller\nfor their reviews. This work was supported by the Caltech Tectonic\nObservatory.", revision_no = "20", abstract = "Africa-North America-Eurasia plate circuit rotations, combined with Red Sea rotations and new estimates of crustal shortening in Iran define the Cenozoic history of the Neotethyan ocean between Arabia and Eurasia. The new constraints indicate that Arabia-Eurasia convergence has been fairly constant at 2 to 3 cm/yr since 56 Ma with slowing of Africa-Eurasia motion to <1 cm/yr near 25 Ma, coeval with the opening of the Red Sea. Ocean closure occurred no later than 10 Ma, and could have occurred prior to this time only if a large amount of continental lithosphere was subducted, suggesting that slowing of Africa significantly predated the Arabia-Eurasia collision. These kinematics imply that Africa's disconnection with the negative buoyancy of the downgoing slab of lithosphere beneath southern Eurasia slowed its motion. The slow, steady rate of northward subduction since 56 Ma contrasts with strongly variable rates of magma production in the Urumieh-Dokhtar arc, implying magma production rate in continental arcs is not linked to subduction rate.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/45140, title ="Pacific-North America plate motion and opening of the Upper Delfín basin, northern Gulf of California, Mexico", author = "Oskin, Michael and Stock, Joann", journal = "Geological Society of America Bulletin", volume = "115", number = "10", pages = "1173-1190", month = "October", year = "2003", doi = "10.1130/B25154.1", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140423-095857093", note = "© 2003 Geological Society of America. Data Repository item 2003134. Manuscript received by the Society 18 March 2002. \nRevised manuscript received 26 December 2002. Manuscript accepted 17 February 2003. Support was provided by National Science Foundation grants EAR-9614674 and EAR-0001248 and a grant from the University of California MEXUS program. We appreciate the support of Jaime\nRoldán-Quintana and Carlos González-Leόn, of the\nUniversidad Nacional Autόnoma de México. Permission\nto enter Isla Tiburόn was granted by the\nSecretaria de Medio Ambiente y Recursos Naturales\nand the Cumcaác (Seri) Indian Tribe. Prescott College\nResearch Station. Bahía Kino, generously provided\nlogistical support during field studies. We are\nespecially grateful to our Cumcaác guide. Ernesto\nMolina, Scott Dobner, Ivlatt Bachman, Robert Houston,\nJason Wise, Naomi Marks, and Lesley Perg assisted\nwith field studies. Discussions with Gary\nAxen, Arturo Martín-Barajas. Elizabeth Nagy, and\nClaudia Lewis, and reviews by Paul Umhoefer and\nJohn Fletcher contributed to the development of this\npaper. California Institute of Technology Publication\n#8869.", revision_no = "15", abstract = "Correlation of conjugate rifted margins of the Upper Delfín basin constrains the timing and amount of transtensional opening along the Pacific–North America plate boundary in the northern Gulf of California. Lithologic, geochemical, paleomagnetic, and geochronologic data from a set of four ignimbrites, consisting of eight distinctive cooling units, are shown to correlate from northeastern Baja California to Isla Tiburón and adjacent areas of western Sonora. These matching ignimbrites are the ca. 12.6 Ma tuff of San Felipe, the 6.3 ± 0.2 Ma tuffs of Mesa Cuadrada (Tmr3 and Tmr4), the tuffs of Dead Battery Canyon (Tmr5), and the 6.1 ± 0.5 Ma tuffs of Arroyo El Canelo. Offset distributions and facies patterns of these ignimbrites support 255 ± 10 km of opening between conjugate rifted margins of the Upper Delfín basin. Addition of deformation from the continental margins of this basin indicates at least 276 ± 13 km of Pacific–North America plate motion between coastal Sonora and the main gulf escarpment in Baja California since ca. 6 Ma; a further 20 ± 10 km of northwestward displacement of Isla Tiburón relative to coastal Sonora occurred sometime after 12.6 Ma. These reconstructions agree with earlier estimates of slip across the Gulf of California and on the San Andreas fault system of southern California, but require that the Pacific–North America plate boundary became localized in the gulf at ca. 6 Ma. The restored continental margins of the Upper Delfín basin show that only a 20–25 km width of upper continental crust has foundered beneath this part of the northern Gulf of California. This result suggests that most of the crustal area formed by opening of the Upper Delfín basin was either exhumed from lower-crustal levels or is new transitional oceanic crust. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/21644, title ="Hotspots Come Unstuck", author = "Stock, Joann M.", journal = "Science", volume = "301", number = "5636", pages = "1059-1060", month = "August", year = "2003", issn = "0036-8075", url = "https://resolver.caltech.edu/CaltechAUTHORS:20110107-085232264", note = "© 2003 American Association for the Advancement of Science. \n\nThis paper represents contribution number 8968,\nDivision of Geological and Planetary Science,\nCalifornia Institute of Technology. The work was supported\nby NSF grant OPP 0126334.", revision_no = "13", abstract = "Volcanic hotspots are widely believed to be caused by fixed volcanic sources deep in the mantle. In her Perspective, Stock highlights the report by Tarduno et al., whose paleomagnetic data cast doubt on the fixity of the hotspot underlying the Hawaiian-Emperor seamounts. The data suggest that not only plate motion but also mantle flow have determined the latitudes of the islands and seamounts in the chain. With current data, it is difficult to say whether the base of the hotspot has remained fixed or whether it is a third variable determining the motion of surface volcanism with time. \n\n", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/45882, title ="Active deformation and shallow structure of the Wagner,\nConsag, and Delfín Basins, northern Gulf of California, Mexico", author = "Persaud, Patricia and Stock, Joann M.", journal = "Journal of Geophysical Research B", volume = "108", number = "B7", pages = "Art. No. 2355", month = "July", year = "2003", doi = "10.1029/2002JB001937", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140522-093031612", note = "© 2003 American Geophysical Union. Article first published online: 31 Jul 2003. Manuscript Accepted: 25 Nov 2002.\nManuscript Revised: 3 Oct 2002. Manuscript Received: 20 Apr 2002. We thank the captain and the crew of the B/O Francisco de Ulloa, as well as Peter Buhl, Sergio Paz, Jose Luis Garcia Puga, and Erich Scholz for making the data collection process successful. We are extremely grateful to Joyce Alsop for her invaluable help and support in processing the seismic data. We thank Julie Nazareth for reviewing early drafts of this manuscript and Uri ten Brink along with two anonymous reviewers for providing thorough reviews of the submitted manuscript, though we remain solely responsible for the ideas contained herein. This research was supported by US National Science Foundation grants OCE-9730790 to Caltech and OCE-9730569 to LDEO, and by CONACYT grant 26669-T to CICESE. We thank PEMEX Exploración y Producción for the permit to use the well data from the northern Gulf of California. Contribution 8863, Division of Geological and Planetary Sciences, California Institute of Technology. Lamont-Doherty Earth Observatory contribution 6385.", revision_no = "14", abstract = "Oblique rifting began synchronously along the length of the Gulf of California at 6 Ma, yet there is no evidence for the existence of oceanic crust or a spreading transform fault system in the northern Gulf. Instead, multichannel seismic data show a broad shallow depression, ∼70 × 200 km, marked by active distributed deformation and six ∼10-km-wide segmented basins lacking well-defined transform faults. We present detailed images of faulting and magmatism based on the high resolution and quality of these data. The northern Gulf crust contains a dense (up to 18 faults in 5 km) complex network of mainly oblique-normal faults, with small offsets, dips of 60–80° and strikes of N-N30°E. Faults with seafloor offsets of tens of meters bound the Lower and two Upper Delfín Basins. These subparallel basins developed along splays from a transtensional zone at the NW end of the Ballenas Transform Fault. Twelve volcanic knolls were identified and are associated with the strands or horsetails from this zone. A structural connection between the two Upper Delfín Basins is evident in the switching of the center of extension along axis. Sonobuoy refraction data suggest that the basement consists of mixed igneous sedimentary material, atypical of mid-ocean ridges. On the basis of the near-surface manifestations of active faulting and magmatism, seafloor spreading will likely first occur in the Lower Delfín Basin. We suggest the transition to seafloor spreading is delayed by the lack of strain-partitioned and focused deformation as a consequence of shear in a broad zone beneath a thick sediment cover.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/49251, title ="Three distinct types of hotspots in the Earth’s mantle", author = "Courtillot, Vincent and Davaille, Anne", journal = "Earth and Planetary Science Letters", volume = "205", number = "3-4", pages = "295-308", month = "January", year = "2003", doi = "10.1016/S0012-821X(02)01048-8 ", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140904-141111178", note = "© 2002 Elsevier Science B.V.\n\nReceived 11 July 2002; received in revised form 17 October 2002; accepted 22 October 2002.\n\nFor their help in discussing various aspects of\nthis paper during its preparation, we thank\nClaude Allègre, Don Anderson, Alain Bonneville,\nBernard Bourdon, Anny Cazenave, Harmon\nCraig, David Evans, Ken Farley, Gilian Foulger,\nStuart Gilder, Marc Javoy, Joe Kirshvink, Stéphane Labrosse, Jean Paul Montagner, Manuel\nMoreira, Jean Paul Poirier, Luc-Emmanuel Ricou,\nBarbara Romanowicz, Norm Sleep (whom we\nalso thank for a preprint on his research on secondary\nhotspots), Bernhard Steinberger, David\nStevenson, and Peter Wyllie. Particular thanks\nare extended to Jeroen Ritsema for extensive\nhelp with the tomographic data, for producing\nFig. 1, and for numerous and useful discussions\nand comments. Norman Sleep and an anonymous\nreviewer are thanked for their comments. V.C. is\nparticularly grateful to the California Institute of\nTechnology and to its Division of Planetary and\nGeological Sciences for offering a Moore Fellowship\nand the best possible atmosphere to work,\ndiscuss and strengthen friendships. IPGP contribution\nNS number 1852.", revision_no = "14", abstract = "The origin of mantle hotspots is a controversial topic. Only seven (‘primary’) out of 49 hotspots meet criteria aimed at detecting a very deep origin (three in the Pacific, four in the Indo-Atlantic hemisphere). In each hemisphere these move slowly, whereas there has been up to 50 mm/a motion between the two hemispheres prior to 50 Ma ago. This correlates with latitudinal shifts in the Hawaiian and Reunion hotspots, and with a change in true polar wander. We propose that hotspots may come from distinct mantle boundary layers, and that the primary ones trace shifts in quadrupolar convection in the lower mantle.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44977, title ="Marine incursion synchronous with plate-boundary localization in the Gulf of California", author = "Oskin, Michael and Stock, Joann", journal = "Geology", volume = "31", number = "1", pages = "23-26", month = "January", year = "2003", doi = "10.1130/0091-7613(2003)031<0023:MISWPB>2.0.CO;2 ", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140416-103726426", note = "© 2003 Geological Society of America.\n\nReceived 9 July 2002; Revision received 19 September 2002;\nAccepted 22 September 2002.\n\nSupported by National Science Foundation grants\nEAR-9614674 and EAR-0001248 and a grant from the University of California MEXUS program. We also appreciate the support of C. González-León of the Universidad Nacional Autónoma de México. Permission to enter Isla Tiburón was granted by the Secretaría de Medio Ambiente y Recursos Naturales\nand the Cumcaác (Seri) Indian Tribe. E. Molina, C.\nLewis, A. Martín-Barajas, S. Dobner, R. Houston, J. Wise, and L. Perg assisted with field studies. Discussions\nwith J.T. Smith and A. Carreño and reviews by W. Normark and J. Helenes contributed to the development of this paper. California Institute of Technology, Division of Geological and Planetary Sciences contribution 8890.\n", revision_no = "14", abstract = "Volcanic strata on southwest Isla Tiburón define the age of interstratified marine rocks and, through revision of existing correlations, the age of the proto–Gulf of California marine incursion. A 5.7 ± 0.2 Ma ash flow was emplaced at the base of the marine section. A rhyodacite dike and its related lava flow, dated as 11.2 ± 1.3 Ma, 3.7 ± 0.9 Ma, and 4.2 ± 1.8 Ma, intrudes and overlies, respectively, the marine rocks. The 11.2 Ma age, which was the core datum for a middle Miocene proto–Gulf of California origin for the underlying rocks, is discordant with all other isotopic and microfossil ages. An alternative interpretation, utilizing all available geologic and geochronologic data except this discordant age, is that marine strata on Isla Tiburón are latest Miocene to early Pliocene age. Reinterpretation of these strata supports a simplified history of marine incursion into the Gulf of California. Marine rocks as old as 8.2 Ma in the southern Gulf of California indicate an early marine incursion, perhaps flooding a region of more intense proto–Gulf of California continental extension. Flooding of the entire basin by 6.5–6.3 Ma correlates to the sudden onset of significant Pacific–North American plate-boundary motion within the Gulf of California. ", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/45119, title ="Cenozoic volcanism and tectonics of the continental margins of the Upper Delfín basin, northeastern Baja California and western Sonora", author = "Oskin, Michael and Stock, Joann", number = "374", pages = "421-438", month = "January", year = "2003", doi = "10.1130/0-8137-2374-4.421", isbn = "9780813723747", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140422-142537032", note = "© 2003 Geological Society of America.\nManuscript accepted by the Society June 2, 2003.\n\nThis work was supported by National Science Foundation\ngrants EAR-9614674 and EAR-0001248. We also appreciate\nthe support of C. González-León of the Universidad Nacional\nAutónoma de México. Permission to enter Isla Tiburón was\ngranted by the Secretaría de Medio Ambiente y Recursos Naturales\nand the Cumcaác (Seri) Indian Tribe. E. Molina, C. Lewis,\nS. Dobner, R. Houston, N. Marks, J. Wise, and L. Perg assisted\nwith field studies. Discussions with C. Lewis, E. Nagy, A. Martín-\nBarajas, and R. Dorsey contributed to development of this\npaper, and reviews by D. Kimbrough and R. Dorsey substantially\nimproved the manuscript and figures. California Institute\nof Technology, Division of Geological and Planetary Sciences\ncontribution #8868.", revision_no = "17", abstract = "Pre- and syn-rift stratigraphy of conjugate rifted margins of the Upper Delfín\nbasin provides a rare opportunity to explore proximal relationships between the loci\nof volcanism and rifting during formation of new ocean basin. The Upper Delfín basin\nis one of a series of youthful, en-echelon ocean basins that accommodate spreading\nbetween the Pacific and North American plates in the Gulf of California. Four groups\nof volcaniclastic stratigraphy are described from the Baja California rifted margin\nfrom the Pucrtecitos Volcanic Province to the Sierra San Felipe and from the conjugate\nSonora rifted margin from Isla Tiburón to the adjacent mainland coastal\nregion. Excluding the uppermost post-6 Ma group, these strata predate opening of\nthe Upper Delfín basin and thus similar facies relationships occur on both conjugate\nrift margins. Pre-rift, mostly arc-related volcanism from 21 to 12 Ma built isolated\nvolcanic centers over a regional Eocene(?) erosion surface cut onto pre-Tertiary\nbasement rocks. The Puertecitos Volcanic Province formed as a concentration of arcrelated\nvolcanism with a peak of activity at 18-15 Ma. Rift-related faulting and basin\nformation initiated after 12.6 Ma to the north and cast of the Puertecitos Volcanic\nProvince, but extension largely bypassed the center of the volcanic province. Rather,\nrifting stepped eastward along the Matomi Accommodation Zone, perhaps by taking\nadvantage of crust weakened by prior arc-related volcanism in the Puertecitos Volcanic\nProvince. Later rift-related volca nism localized along intersections of the Mato mi\nAccommodation Zone and north-striking extensional faults. The crustal break that\nopened the Upper Delfín basin ca. 6 Ma coincides with the most voluminous exposures\nof late Miocene syn-rift volcanism and the vent area for 6.7-6.1 Ma rhyolite\nignimbrites that blanketed the region just prior to the onset of marine sedimentation.\nOverall, the pattern of arc- and rift-related volcanism, sedimentation, and faulting on\nthe margins of the Upper Delfín basin indicates a close association between continental\nextension and volcanism. These relationships support that magmatism and crustal\nrift structure evolved as a coupled system to localize Pacific-North America plate\nmotion into the Gulf of California.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44961, title ="Rapid postseismic transients in subduction zones from\ncontinuous GPS", author = "Melbourne, Timothy I. and Webb, Frank H.", journal = "Journal of Geophysical Research B", volume = "107", number = "B10", pages = "Art. No. 2241", month = "October", year = "2002", doi = "10.1029/2001JB000555", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140415-125909434", note = "© 2002 American Geophysical Union.\n\nIssue published online: 22 Oct 2002; Article first published online: 22 Oct 2002; Manuscript Accepted: 9 Jan 2002; Manuscript Revised: 5 Jan 2002; Manuscript Received: 7 May 2001.\n\nWe thank Osvaldo Sanchez of the Autonomous\nUniversity of Mexico (UNAM) for supplying the tide gauge data. Discussion with Jeanne Hardebeck on Coulomb stress transfer was very helpful. Figures were generated with Generic Mapping Tools [Wessel and Smith, 1991]. Jalisco field work was supported under NSF grant EAR-9527810 to J. Stock, while data analysis of subsequent earthquakes was\nsupported under NSF grant EAR-9973191 to T. Melbourne.", revision_no = "12", abstract = "Continuous GPS time series from three of four recently measured, large subduction earthquakes document triggered rapid postseismic fault creep, representing an additional moment release upward of 25% over the weeks following their main shocks. Data from two M_w = 8.0 and M_w = 8.4 events constrain the postseismic centroids to lie down dip from the lower limit of coseismic faulting, and show that afterslip along the primary coseismic asperities is significantly less important than triggered deep creep. Time series for another M_w = 7.7 event show 30% postseismic energy release, but here we cannot differentiate between afterslip and triggered deeper creep. A fourth M_w = 8.1 event, which occurred in the broad Chilean seismogenic zone, shows no postseismic deformation, despite coseismic offsets in excess of 1 m. For the three events which are followed by postseismic deformation, stress transferred to the inferred centroids (at 34, 60, and 36 km depths) by their respective main shock asperities increased reverse shear stress by 0.5, 0.8, and 0.2 bar with a comparatively small decrease in normal stress (0.01 bar), constraining the Coulomb stress increase required to force slip along the metastable plate interface. Deep triggered slip of this nature is invisible without continuous geodesy but on the basis of these earthquakes would appear to constitute an important mode of strain release from beneath the seismogenic zones of convergent margins. These events, captured by some of the first permanent GPS networks, show that deep moment release is often modulated by seismogenic rupture updip and underscore the need for continuous geodesy to fully quantify the spectrum of moment release in great earthquakes.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/34604, title ="Mid-Cretaceous tectonic evolution of the Tongareva triple junction in the southwestern Pacific Basin", author = "Larson, Roger L. and Pockalny, Robert A.", journal = "Geology", volume = "30", number = "1", pages = "67-70", month = "January", year = "2002", doi = "10.1130/0091-7613(2002)030<0067:MCTEOT>2.0.CO;2", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20121001-150237189", note = "© 2002 Geological Society of America.\n\nManuscript received June 1, 2001;\nRevised manuscript received September 20, 2001;\nManuscript accepted October 1, 2001.\nWe thank the personnel on Expeditions Cook-4 and Kiwi-12 for professional\nsupport at sea and J. Mammerickx for helpful discussions. R. Sutherland\nand S. Gulick provided comprehensive and useful reviews. This research is\nsponsored by National Science Foundation grant OCE-9818776 to the University\nof Rhode Island, and by funding from the University of California and the\nCalifornia Institute of Technology.", revision_no = "18", abstract = "The trace of the ridge-ridge-ridge triple junction that connected the Pacific, Farallon, and Phoenix plates during mid-Cretaceous time originates at the northeast corner of the Manihiki Plateau near the Tongareva atoll, for which the structure is named. The triple junction trace extends >3250 km south-southeast, to and beyond a magnetic anomaly 34 bight. It is identified by the intersection of nearly orthogonal abyssal hill fabrics, which mark the former intersections of the Pacific-Phoenix and Pacific-Farallon Ridges. A distinct trough is commonly present at the intersection. A volcanic episode from 125 to 120 Ma created the Manihiki Plateau with at least twice its present volume, and displaced the triple junction southeast from the Nova-Canton Trough to the newly formed Manihiki Plateau. Almost simultaneously, the plateau was rifted by the new triple junction system, and large fragments of the plateau were rafted away to the south and east. The Tongareva triple junction originated ca. 119 Ma, when carbonate sedimentation began atop the Manihiki Plateau. Subsequent spreading rates on the Pacific-Phoenix and Pacific-Farallon Ridges averaged 18–20 cm/yr until 84 Ma.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/45141, title ="Tectonic history of Antarctic seafloor in the Australia-New Zealand-South Pacific sector: implications for Antarctic continental tectonics", author = "Stock, J. M. and Cande, S. C.", number = "35", pages = "251-259", month = "January", year = "2002", isbn = "1877264067", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140423-104037295", note = "© The Royal Society of New Zealand. Last updated\n2012-06-07. We thank Carol Raymond, Bruce Luyendyk, Geoff Rait, and Dick Walcott for helpful reviews of the manuscript. California Institute of Technology, Division of Geological and Planetary Science, contribution number 8692. This research was supported by US National Science Foundation grants OPP-9814579 and OPP-98-1528.", revision_no = "14", abstract = "We review the seafloor spreading record of plate motions adjacent to the Antarctic continent during and after Cretaceous separation of the New Zealand and Australia continental fragments from Antarctica. The earliest seafloor in this region (c. 95-83 Ma) records separation of Australia from Antarctica and separation of the Lord Howe rise from eastern Australia. At this time, continental extension occurred between the Campbell Plateau/Chatham Rise and Marie Byrd Land with oblique subduction of Phoenix plate fragments (Aluk and Bellingshausen) beneath the West Antarctic margin from c. 125ºW to at least 90ºW. Seafloor spreading started first (Chron 34, before 83 Ma) in the mouth of the rift, between the Chatham Rise and the Bellingshausen plate, and later (Chron 33, c. 79 Ma) between the Campbell Plateau and Marie Byrd Land, joining the Tasman sea ridge to the southwest Pacific spreading centre. Subsequent tectonic events include: (1) <50 km of rifting of the seafloor adjacent to Marie Byrd Land along the northeast-trending Iselin trough, east of the Iselin Bank, from Chrons 27 to 24 (61-55 Ma); (2) propagation of the southeast Indian Ridge between the south Tasman Rise and Victoria Land to join the Tasman Sea spreading centre by Chron 27 (61 Ma); (3) capture of the Bellingshausen plate by West Antarctica by about Chron 27; (4) 150-180 km of separation between East Antarctica and West Antarctica (Iselin Bank) centred on the NNW-trending Adare trough between Chrons 18 and 9 (40-27 Ma). These observations predict, first, that the West Antarctic margin at 125ºW was the site of a triple junction from at least 84 to 61 Ma, with Phoenix plate annihilation and expected tectonics of West Antarctica in many ways analogous to breakup of the Farallon plate and its effects on western North America. Second, northern Victoria Land may exhibit unique tectonics compared to elsewhere along this part of the Antarctic margin because it lay in a continental strike-slip regime, sliding against continental crust of the Australia plate (western south Tasman Rise) until Eocene time. Finally, the 150+ km of Oligocene seafloor formed at the Adare Trough implies a significant extensional event of this age farther south in the Ross Sea, in agreement with results from recent drilling at Cape Roberts hole CRP-3.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44965, title ="Homogeneous vs heterogeneous subduction zone models: Coseismic and postseismic deformation", author = "Masterlark, T. and DeMets, C.", journal = "Geophysical Research Letters", volume = "28", number = "21", pages = "4047-4050", month = "November", year = "2001", doi = "10.1029/2001GL013612", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140415-145647377", note = "© 2001 American Geophysical Union. \n\nReceived: 8 Jun 2001. Accepted: 21 Aug 2001. This project was funded by NSF EAR9909321 (CD), EAR9909377 (JS), and the Lewis Weeks endowment (CD).", revision_no = "11", abstract = "A finite-element model (FEM) incorporating geologic properties characteristic of a subduction zone is compared with FEMs approximating homogeneous elastic half-spaces (HEHS)s to investigate the effect of heterogeneity on coseismic and postseismic deformation predictions for the 1995 Colima-Jalisco M_w =8.0 earthquake. The FEMs are used to compute a coefficient matrix relating displacements at observation points due to unit dislocations of contact-node pairs on the fault surface. The Green's function responses are used to solve the inverse problem of estimating dislocation distributions from coseismic GPS displacements. Predictions from the FEM with heterogeneous material properties, loaded with either of the HEHS dislocation distributions, significantly overestimate coseismic displacements. Postseismic deformation predictions are also sensitive to the coseismic dislocation distribution, which drives poroelastic and viscoelastic relaxation. FEM-generated Green's functions, which allow for spatial variations in material properties, are thus preferable to those that assume a simple HEHS because the latter leads to dislocation distributions unsuitable for predicting the postseismic response.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44963, title ="Slip kinematics and dynamics during and after the 1995 October 9 M_w=8.0 Colima–Jalisco earthquake, Mexico, from GPS geodetic constraints", author = "Hutton, W. and DeMets, C.", journal = "Geophysical Journal International", volume = "146", number = "3", pages = "637-658", month = "September", year = "2001", doi = "10.1046/j.1365-246X.2001.00472.x", issn = "0956-540X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140415-132949940", note = "© 2001 RAS. Accepted 2001 April 6. Received 2001 April 14; in original form 2000 October 24. Article first published online: 20 Dec 2001. Numerous individuals assisted our field and modelling efforts, including students from Caltech, UC-Berkeley, University of Guadalajara, UNAM, and UW-Madison. We thank Ian Carmichael and UNAM for their foresight in funding the initial network installation and occupation. We thank Dra. Bertha Marquez-Azua for her tireless and cheerful assistance, Bill Unger for his meticulous field work, and Dr. Tim Melbourne and Dr. Pedro Zarate del Valle. We thank Bill, Ana, and Eduardo Douglass for their hospitality, personal vehicles, and memorable stays in their palapa. We thank Ken Hudnut and Sean Larsen for dispensing computer code and test cases. We thank Dr. Jaime Arturo Paz Garcia, Director General of Proteccion Civil of Jalisco, for providing vehicles and drivers, and the University of Guadalajara for providing field vehicles. Finally, we thank Brett Baker and UNAVCO for providing equipment and field assistance. Constructive reviews were given by Steve Cohen, Greg Lyzenga, and Steven Ward, and figures were produced using Generic Mapping Tool software (Wessel and Smith, 1991). This work was funded using grants from CONACYT (4933-T9406) and NSF (EAR9527810-JS; EAR9526419-CD). ", revision_no = "12", abstract = "We use horizontal and vertical crustal displacements derived from GPS measurements at 26 sites in western Mexico to study the coseismic and post-seismic kinematics and dynamics of the 1995 October 9 (M_w=8.0) Colima–Jalisco earthquake along the Middle America Trench. The measurements bracket the entire landward edge of the approximately 150 km long rupture zone and span a 4 yr period for most sites. We solve for the temporal evolution of slip along the subduction interface by inverting GPS displacements for the coseismic and four post-seismic intervals (March 1995–March 1999), subject to the assumption that the crust responds elastically to slip along a shallow-dipping, curved subduction interface. Coseismic rupture of up to 5 m was largely focused above depths of 20 km and was limited to a 120–140 km long segment of the subduction zone. Within one week of the earthquake, post-seismic slip migrated downdip to depths of 16–35 km, where it has since decayed logarithmically. We also find evidence for shallow aseismic slip during 1996 or early 1997 northwest of the coseismic rupture zone and increasingly widespread relocking of shallow regions of the subduction interface after early 1997. The relative lack of afterslip in shallow regions of the subduction interface suggests that the interface lies in the unstable frictional regime and hence is strongly coupled between earthquakes. By 1999, the cumulative slip moment associated with post-seismic slip equaled ∼70 per cent of the coseismic moment, with nearly all of this slip occurring downdip from the coseismic rupture zone. The migration of slip after the earthquake to a deeper and presumably velocity-strengthening area of the subduction interface and the logarithmic decay of afterslip conform to the qualitative and quantitative predictions of a model in which the fault kinematics are prescribed by rate- and state-variable frictional laws. However, misfits to the geodetic displacements exceed the average displacement uncertainties for all epochs, implying one or more of the following: (1) the elastic response is heterogeneous due to slip along unmodelled upper crustal faults or variations in the elastic properties of the crust; (2) other post-seismic mechanisms such as viscoelastic or poroelastic effects contribute to or possibly dominate the post-seismic response; (3) we have underestimated the uncertainties in the GPS displacements.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44971, title ="Evolution of the Malvinas Plate South of Africa", author = "Marks, K. M. and Stock, J. M.", journal = "Marine Geophysical Researches", volume = "22", number = "4", pages = "289-302", month = "July", year = "2001", doi = "10.1023/A:1014638325616", issn = "0025-3235", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140416-090645328", note = "© 2002 Kluwer Academic Publishers. Received 20 March 2001; accepted 2 October 2001. This revised version was published online in November 2006 with corrections to the Cover Date. The comments of two anonymous reviewers greatly\nimproved this manuscript. We thank Steve Cande for\ndigital magnetic anomaly identifications in the South\nAtlantic Ocean. J. Stock’s participation was supported\nby NSF grant OPP-9814579. California Institute of\nTechnology, Division of Geological and Planetary\nSciences, contribution 8839. Images of the reconstructions\nare available on the Worldwide Web site\nhttp://ibis.grdl.noaa.gov/SAT/kmm/pubs.kmm.html.", revision_no = "13", abstract = "We confirm that a Malvinas Plate is required in the Agulhas Basin during the Late Cretaceous because: (1) oblique Mercator plots of marine gravity show that fracture zones generated on the Agulhas rift, as well as the Agulhas Fracture Zone, do not lie on small circles about the 33o-28y South America-Africa stage pole and were therefore not formed by South America-Africa spreading, (2) the 33o-28y South America-Africa stage rotation does not bring 33o magnetic anomalies on the Malvinas Plate into alignment with their conjugates on the African Plate, and (3) errors in the 33o-28y South America-Africa stage rotation cannot account for the misalignment. We present improved Malvinas-Africa finite rotations determined by interpreting magnetic anomaly data in light of fracture zones and extinct spreading rift segments (the Agulhas rift) that are clearly revealed in satellite-derived marine gravity fields covering the Agulhas Basin. The tectonic history of the Malvinas Plate is chronicled through gravity field reconstructions that use the improved Malvinas-Africa finite rotations and more recent South America-Africa and Antarctica-Africa finite rotations. Newly-mapped triple junction traces on the Antarctic, South American, Malvinas, and African Plates, combined with geometric and magnetic constraints observed in the reconstructions, enable us to investigate the locations of the elusive western and southern boundaries of the Malvinas Plate.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44953, title ="Rapid localization of Pacific–North America plate motion in the Gulf of California", author = "Oskin, Michael and Stock, Joann", journal = "Geology", volume = "29", number = "5", pages = "459-462", month = "May", year = "2001", doi = "10.1130/0091-7613(2001)029<0459:RLOPNA>2.0.CO;2", issn = "0091-7613", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140415-110426833", note = "© 2001 Geological Society of America. Manuscript received August 17, 2000. Revised manuscript received January 22, 2001. Manuscript accepted January 29, 2001. Support was provided by National Science Foundation grants EAR-9614674 and EAR-0001248. We thank R.G. Gastil and C. Lewis for guidance with initial reconnaissance in Sonora, and J. Kirschvink for use of the Caltech Paleomagnetics Laboratory.\nWe also appreciate the support of J. Roldán-Quintana and C. González-Leόn of the Universidad Nacional Autόnoma de México. Permission to enter Isla Tiburόn was granted by the Secretaría de Medio Ambiente y Recursos Naturales and the Cumcaác (Seri) Indian Tribe. Prescott College Research Station, Bahia Kino, generously provided logistical\nsupport during field studies. We are especially grateful\nto our Cumcaác guide, Ernesto Molina. S. Dobner,\nM. Bachman, R. Houston, J. Wise, N. Marks,\nand L. Perg assisted with field studies. Discussions\nwith G. Axen, E. Nagy, and C. Lewis and reviews\nby J. Vallance and J. Ruiz contributed to the development\nof this paper. California Institute of Technology,\nDivision of Geological and Planetary Sciences\nContribution 8712.", revision_no = "14", abstract = "Correlation of late Miocene volcaniclastic strata across the northern Gulf of California shows that the Pacific–North America plate boundary localized east of the Baja California peninsula ca. 6 Ma. Dextral offset of the 12.6 Ma Tuff of San Felipe and a pair of overlying ca. 6.3 Ma pyroclastic flows indicate at least 255 ± 10 km of displacement along an azimuth of 310°. Isopach and facies trends of the Tuff of San Felipe support no more than a few tens of kilometers of additional dextral displacement between 12.6 and 6.3 Ma. These constraints indicate that nearly all of the dextral displacement between the Pacific and North American plates prior to 6.3 Ma was accommodated outside of the gulf region, and by 4.7 Ma, the plate boundary motion was localized in the Gulf of California. Although continental extension has accounted for a component of plate boundary motion in northwestern Mexico since cessation of subduction offshore of southern Baja California at 12.5 Ma, transfer of Baja California to the Pacific plate was delayed by at least 6–7 m.y. ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44960, title ="Structural controls on the continent-ocean transition in the northern Gulf of California", author = "Nagy, Elizabeth A. and Stock, Joann M.", journal = "Journal of Geophysical Research B", volume = "105", number = "B7", pages = "16251-16269", month = "July", year = "2000", doi = "10.1029/1999JB900402", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140415-125536360", note = "© 2000 American Geophysical Union.\n\nManuscript Accepted: 5 Nov 1999; Manuscript Received: 12 Apr 1999.\n\nWe thank Gary Axen, John Fletcher, and Associate Editor Walter Mooney for constructive thoughtful reviews which clarified the presentation of several key points. This work was supported by NSF grants EAR-9218381, EAR-9296102, and EAR-9614674, and is contribution 8620 from the Division of Geological and Planetary Sciences of the California Institute of Technology.", revision_no = "14", abstract = "In the Gulf of California the Pacific-North America plate boundary changes character from an oceanic-type spreading center and transform fault system (to the south) to a region of diffuse continental deformation (to the north). The presence of spreading centers commonly inferred in the northernmost gulf is not supported by bathymetric, heat flow, gravity, or seismic data which indicate significant differences north and south of latitude ∼30°N. We suggest instead that north of ∼30°N a continent-ocean transition begins which we name the Wagner Transition Zone (WTZ). Diffuse deformation characterizes the WTZ where slip occurs along reactivated north to NNW striking normal faults developed during late Miocene or Pliocene ENE directed extension. Transtensional deformation varies from ENE directed extension along dip-slip faults in the west to dextral shear along the coast to dextral-oblique slip along inferred north to NNW striking faults submerged in the northern gulf. By accounting for rotational and extensional plate motion deformation in northeastern Baja California, vector constraints require that submerged structures accommodate ∼30 mm/yr of slip in a direction slightly clockwise of the relative plate motion direction. The juxtaposition of the discrete spreading center system in the central gulf with the diffuse WTZ appears to have been a stable configuration since 4–6 Ma, perhaps controlling the evolution of spreading center jumps between Upper and Lower Tiburón and Delfin basins due to the juxtaposition of kinematically partitioned structural domains. Different histories of prerift extension and subduction-related arc magmatism along the length of the gulf, partly related to the migration of the Rivera triple junction, may explain the location of the continent-ocean transition.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44934, title ="Morphology and origin of the Osbourn Trough", author = "Billen, Magali I. and Stock, Joann", journal = "Journal of Geophysical Research B", volume = "105", number = "B6", pages = "13481-13489", month = "June", year = "2000", doi = "10.1029/2000JB900035 ", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140414-140339355", note = "© 2000 American Geophysical Union.\n\nReceived July 22, 1999; revised December 16, 1999; accepted January 26, 2000.\n\nThis research was supported by\nNSF OPP 9317318 and OCE 9416779. Dallas Abbott,\nBruce Luyendyk and Associate Editor Keith Louden provided\nhelpful reviews of this paper. We thank Antarctic\nSupport Associates, the crew and Captain Joe Borkowski\nof the RVIB Nathaniel B. Palmer, and Suzanne O'Hara for\ntheir help in collecting and processing the data, and Steve\nCande for his helpful comments. California Institute of Technology,\nDivision of Geological and Planetary Science, contribution\n8618.", revision_no = "11", abstract = "The Osbourn Trough is a 900 km long, east-west trending gravity low, visible in satellite altimetry data, which intersects the Tonga Trench at 25°30′S. A recent survey collected gravity, magnetic, echo sounder, and swath bathymetry data on three adjacent, north-south trending ship tracks centered on the trough. The linear gravity low is 20–30 mGal less than the regional value and is accompanied by a flat-lying, 200–500 m deep sediment-filled valley. Swath bathymetry images reveal several parallel, east-west trending linear ridges and valleys on either side of the main trough as well as other morphologic features characteristic of relict spreading centers, including a prominent inside corner high and possible pseudo-fault trace. The presence of magnetic anomalies (possibly anomalies 33 and 32) suggests that the seafloor here was formed after the end of the Cretaceous Normal Superchron (anomaly 34). These data support the conclusion that this trough is a spreading center, which stopped spreading in Late Cretaceous time. The existence of this feature has important implications for tectonic reconstructions in this region. The Osbourn Trough could be part of the fossil spreading center between the Pacific Plate and a fragment of the Phoenix Plate, the Bellingshausen Plate. This would require the seafloor between the Osbourn Trough and the Chatham Rise to the south to be a remnant fragment of the Bellingshausen Plate. This remnant may have joined to the Pacific Plate when the Hikurangi Plateau entered the Gondwana subduction zone at the Chatham Rise possibly causing the cessation of spreading on the Osbourn Trough.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44998, title ="An age constraint on Gulf of California rifting from the Santa Rosalía basin, Baja California Sur, Mexico", author = "Holt, John W. and Holt, Elizabeth W.", journal = "Geological Society of America Bulletin", volume = "112", number = "4", pages = "540-549", month = "April", year = "2000", doi = "10.1130/0016-7606(2000)112<0540:AACOGO>2.3.CO;2", issn = "0016-7606", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140417-091012374", note = "© 2000 Geological Society of America. Manuscript received by the society July 24, 1998. Revised manuscript received March 4, 1994. Manuscript accepted April 6, 1999. This is contribution 8637 or the Caltech Division of Geological and Planetary Sciences. This work was supported by National Science Foundation grants EAR-9019289, EAR-9419041, and EAR-9296102. We are pleased to thank Joseph L. Kirschvink for use of the Cal tech Paleomagnetics Laboratory, Mahmoud Chaudry for preparing mineral separates, Marty Grove at UCLA for performing the argon measurements, Elizabeth Nagy for performing initial argon statistics, Xavier Quidelleur for assisting in blank corrections and additional statistical analyses, and Rob Coe for the use of his rock magnetic facilities at University of California, Santa Cruz. We thank Laurie Brown, Bob Butler, and Kenneth Kodama for their careful reviews and suggestions. Also, muchas gracias to the hombre with the huge tractor who pulled our truck across the flooding river at Colonia San Vicente Guerrero.", revision_no = "15", abstract = "Marine rocks of the Santa Rosalía basin, Baja California Sur, were sampled in a pilot study to determine their suitability for magnetostratigraphy and geochronology with the goal of providing an age constraint on Gulf of California rifting. Progressive demagnetization of samples from the Boleo Formation, the earliest marine sequence overlying the deeply eroded basement, reveals a high-coercivity characteristic remanent magnetization (ChRM) in addition to a low-coercivity overprint. The ChRM appears to be a primary magnetic remanence with stratigraphically bound normal- and reversed-polarity directions. A single ^(40)Ar/^(39)Ar isotopic age of 6.76 ± 0.90 Ma (2σ) was obtained for the cinta colorada, a tephra deposit of reversed paleomagnetic polarity within the Boleo Formation. The age of the cinta colorada is refined by calculating isotopic age probabilities for each of the reversed-polarity intervals of the geomagnetic polarity time scale (GPTS) in the ±2σ range 5.86–7.66 Ma. The interval with the highest probability is 6.57–6.94 Ma. In conjunction with the isotopic age, preliminary magnetostratigraphy of the Boleo Formation is correlated with the GPTS in order to further delineate the onset of marine sedimentation. The most likely correlation yields an age of 6.93–7.09 Ma (GPTS subchron C3Bn) for the base of the Boleo Formation and 6.14–6.27 Ma for the top. This correlation, indicating an average sedimentation rate of 28 ± 4 cm/k.y., could be significantly altered if a more thorough magnetostratigraphy proved the existence of additional polarity intervals in the Boleo Formation. However, even if the isotopic age of the cinta colorada is used as the only age constraint, the result is consistent with data from the northern Gulf of California and shows that rifting started much earlier than the ca. 3.6 Ma commencement of sea-floor spreading at the mouth of the Gulf of California. The deposition of the Boleo Formation was probably related to an early phase of gulf rifting caused by a change in Pacific–North American plate motions.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/77002, title ="Introduction to special issue: \"The influence of plate interaction on post-Laramide magmatism and tectonics in Mexico\"", author = "Ferrari, Luca and Stock, Joann M.", journal = "Tectonophysics", volume = "318", number = "1-4", pages = "vii-ix", month = "March", year = "2000", doi = "10.1016/S0040-1951(99)00303-0", issn = "0040-1951", url = "https://resolver.caltech.edu/CaltechAUTHORS:20170427-105445312", note = "© 2000 Elsevier Science B.V. \n\nAvailable online 10 April 2000. \n\nWe are indebted to Tectonophysics editor Terry Engelder who supervised the editorial process and provided useful advice. We would also like to acknowledge all the scientists who helped us in the review process with timely response and careful examination of the original manuscripts. They are (in alphabetical order): Jorge Aranda-Gomez (Instituto de Geologia, UNAM, Campus Juriquilla, Queretaro, Mexico); Tanya Atwater (University of California at Santa Barbara, USA); Gary Axen (University of California at Los Angeles, USA); Charles Bacon (US Geological Survey, Menlo Park, CA, USA); William Bandy (Instituto de Geofı́sica, UNAM, Mexico City, Mexico); Kenneth Cameron (University of California at Santa Cruz, USA); William Dickinson (University of Arizona, Tucson, USA); Apto Gogichaishvili (University of Montpellier, France); Toshiaki Hasenaka (Akita University, Japan); Claudia J. Lewis (Los Alamos National Laboratory, Los Alamos, USA); José Luis Macı́as (Instituto de Geofı́sica, UNAM, Mexico City, Mexico); Arturo Martı́n-Barajas (CICESE, Ensenada, Baja California, Mexico); William MacDonald (State University of New York, Binghamton, USA); Fred McDowell (University of Texas, Austin, USA); Jorge Nieto-Obregón (Facultad de Ingenierı́a, UNAM, Mexico City, Mexico); Angel Nieto-Samaniego (Instituto de Geologia, UNAM, Campus Juriquilla, Queretaro, Mexico); Josep Pares (Universidad Complutense de Madrid, Spain); Steve Reynolds (University of Arizona, Tucson, USA); Joaquin Ruiz (University of Arizona, Tucson, USA); Richard Sedlock (San José State University, San José, USA); Christian Teyssier (University of Minnesota, Minneapolis, USA), Gustavo Tolson-Jones (Instituto de Geologı́a, UNAM, Mexico City, Mexico); Peter Weigand (California State University at Northridge, USA); Douglas Wilson (University of California at Santa Barbara, USA); Xixi Zhao (University of California at Santa Cruz, USA).", revision_no = "9", abstract = "Among convergent margins, Mexico is an excellent site for studying along-strike variation in plate tectonics at the trench and its effect on the accompanying volcanism and tectonics in the overriding plate. The progressive fragmentation and consumption of the Farallon plate and the interaction between the Pacific and North America plates during the Cenozoic produced some unique geologic features. These include the Sierra Madre Occidental, one of the largest silicic igneous provinces on Earth, and the Trans-Mexican Volcanic Belt, a complex continental volcanic arc underlain by two of the youngest slabs in the world. In addition, extension occurred concurrently in much of the region affected by volcanism, producing a significant part of the southern Basin and Range province, and the reactivation of older basement structures which controlled the emplacement of volcanism.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44941, title ="Cenozoic motion between East and West Antarctica", author = "Cande, Steven C. and Stock, Joann M.", journal = "Nature", volume = "404", number = "6774", pages = "145-150", month = "March", year = "2000", doi = "10.1038/35004501", issn = "0028-0836", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140415-074414969", note = "© 2000 Macmillan Magazines Ltd. Received 30 August 1999; accepted 24 January 2000. We thank the captains, officers, crews and scientific staff of the RV Ewing and RVIB Palmer\nfor their dedicated efforts. We also thank B. Luyendyk and R. Sutherland for helpful comments. The project was funded by grants from the National Science Foundation (S. C. C. and J. M. S.).", revision_no = "20", abstract = "The West Antarctic rift system is the result of late Mesozoic and Cenozoic extension between East and West Antarctica, and represents one of the largest active continental rift systems on Earth. But the timing and magnitude of the plate motions leading to the development of this rift system remain poorly known, because of a lack of magnetic anomaly and fracture zone constraints on seafloor spreading. Here we report on magnetic data, gravity data and swath bathymetry collected in several areas of the south Tasman Sea and northern Ross Sea. These results enable us to calculate mid-Cenozoic rotation parameters for East and West Antarctica. These rotations show that there was roughly 180 km of separation in the western Ross Sea embayment in Eocene and Oligocene time. This episode of extension provides a tectonic setting for several significant Cenozoic tectonic events in the Ross Sea embayment including the uplift of the Transantarctic Mountains and the deposition of large thicknesses of Oligocene sediments. Inclusion of this East–West Antarctic motion in the plate circuit linking the Australia, Antarctic and Pacific plates removes a puzzling gap between the Lord Howe rise and Campbell plateau found in previous early Tertiary reconstructions of the New Zealand region. Determination of this East–West Antarctic motion also resolves a long standing controversy regarding the contribution of deformation in this region to the global plate circuit linking the Pacific to the rest of the world.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44992, title ="Fast Paleogene Motion of the Pacific Hotspots From Revised Global Plate Circuit Constraints", author = "Raymond, Carol A. and Stock, Joann M.", number = "121", pages = "359-375", month = "January", year = "2000", doi = "10.1029/GM121p0359", isbn = "9780875909790", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140416-153704888", note = "© 2000 American Geophysical Union.\nThis work benefited from discussions\nwith many people, especially Richard Gordon, Bernhard Steinberger,\nTodd Ratcliff, Dietmar Mueller, Chuck DeMets and\nGary Acton. Reviews by B. Steinberger and an anonymous\nreviewer improved the manuscript. GMT software was used to\nproduce the figures (Wessel and Smith, 1991). This research\nwas supported by NSF-OPP-93-17318. Part of the work was\nperformed at the Jet Propulsion Laboratory, California Institute\nof Technology, under contract to the National Aeronautics and\nSpace Administration. California Institute of Technology,\nDivision of Geological and Planetary Sciences, Contribution\nnumber 8688.", revision_no = "15", abstract = "Major improvements in Late Cretaceous-early Tertiary Pacific-Antarctica\nplate reconstructions, and new East-West Antarctica rotations, allow a more\ndefinitive test of the relative motion between hotspots using global plate circuit\nreconstructions with quantitative uncertainties. The hotspot reconstructions,\nusing an updated Pacific-hotspot kinematic model, display significant misfits of\nobserved and reconstructed hotspot tracks in the Pacific and Indian Oceans.\nThe misfits imply motions of 5-80 mm/yr throughout the Cenozoic between the\nAfrican-Indian hotspot group and the Hawaiian hotspot. Previously recognized\nmisfits between reconstructed Pacific plate paleomagnetic poles and those of\nother plates might be accounted for within the age uncertainty of the\npaleomagnetic poles, and non-dipole field contributions. We conclude that the\nderived motion of the Hawaiian hotspot relative to the Indo-Atlantic hotspots\nbetween 61 Ma and present is a robust result. Thus, the Pacific hotspot\nreference frame cannot be considered as fixed relative to the deep mantle. The\nbend in the Hawaiian-Emperor Seamount chain at 43 Ma resulted from a\nspeedup in the absolute motion of the Pacific plate in a westward direction\nduring a period of southward migration of the hotspot. The relationship between\nthe hotspot motion and plate motion at Hawaii suggests two possible scenarios:\nan entrainment of the volcanic sources in the asthenosphere beneath the rapidly\nmoving plate while the hotspot source drifted in a plate-driven counterflow\ndeeper within the mantle, or drift of the hotspot source which was independent\nof the plate motion, but responded to common forces, producing synchronous\nchanges in hotspot and plate motion during the early Tertiary.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44994, title ="Mesozoic/Cenozoic Tectonic Events Around Australia", author = "Müller, R. Dietmar and Gaină, Carmen", number = "121", pages = "161-188", month = "January", year = "2000", doi = "10.1029/GM121p0161", isbn = "9780875909790", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140416-154731979", note = "© 2000 American Geophysical Union.\nWe thank John Veevers, Richard Gordon, and\nan anonymous reviewer for constructive comments which improved the quality of the manuscript. This work was supported by the Australian Research Council, the Australian Geological Survey Organization and the\nUniversity of Sydney.", revision_no = "16", abstract = "We use an absolute and relative plate motion model for the plates around\nAustralia to identify major plate tectonic events, evaluate their causes, and investigate\ntheir effects on anomalous intraplate subsidence or uplift and on the history\nof oceanic crustal accretion. An event at ~136 Ma is marked by the onset of sea\nfloor spreading between Greater India and Australia. At about this time long-lived\nsubduction east of Australia ceased, probably due to subduction of the\nPhoenix-Pacific spreading ridge, changing this plate boundary to a transform\nmargin. Between 130 and 80 Ma, Australia and East Antarctica moved eastward\nin the Atlantic-Indian mantle hotspot reference frame. This can be plausibly\nlinked to ridge push from the NW -SE oriented spreading center NW of Australia\nand to the inferred geometry and continued subduction of the Phoenix plate\nbeneath the West Antarctic margin. A drastic change in spreading direction\nbetween the Indian and Australian plates from NE-SW to N-S occurred at about\n99 Ma, possibly caused by a change in absolute motion of the Pacific Plate.\nChron 27 (~61 Ma) marks the onset of relative motion between East and West\nAntarctica, and a change in the relative motion between Australia and Antarctica.\nIt may be linked to the subduction of a segment of the Neo-Tethyan Ridge. Both\nevents caused anomalous subsidence on the Northwest Shelf of Australia. The\nalmost stationary position of Australia w.r.t. the mantle from -80 Ma to -40 Ma\nmay reflect the progressive subduction of the Pacific-Phoenix ridge to the east of\nNew Zealand preceding 80 Ma, resulting in a diminished trench suction force east\nof Australia. Preliminary reconstructions to close the Pacific-Australian plate\ncircuit based on recently collected geophysical data indicate that a tectonic event\nat 43 Ma may mark the onset of renewed subduction east of Australia. At the\nsame time spreading in the Wharton Basin between India and Australia ceased,\nand tectonic reactivation is recorded in the Bass Strait. Excess late Tertiary subsidence\non the northwest shelf of >500 m matches the anomalous depth of the Argo abyssal plain ocean floor. This anomalous subsidence may express largescale\nintraplate deformation in the Indian Ocean. Asymmetries in oceanic crustal\naccretion around Australia are caused mainly by hotspot-ridge and coldspot-ridge\ninteraction.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/45097, title ="Relation of the Puertecitos Volcanic Province, Baja California, Mexico, to development of the plate boundary in the Gulf of California", author = "Stock, Joann M.", number = "334", pages = "143-156", month = "January", year = "2000", doi = "10.1130/0-8137-2334-5.143", isbn = "9780813723341", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140422-074216122", note = "© 2000 Geological Society of America.\nManuscript accepted by the Society August 31, 1998.\nThis research was supported by National Science Foundation\ngrant EAR-9296102. Gary Axen and Paul Umhoefer provided\nhelpful comments on an earlier version of this paper.\nDivision of Geological and Planetary Sciences, California Institute\nof Technology. Contribution 5632.", revision_no = "16", abstract = "The Puertecitos Volcanic Province is a late Miocene and Pliocene ignimbrite field\ncovering an area of ~2600 km^2, with an estimated erupted volume of at least 500 km^3. It\nis unique on the Baja California Peninsula in terms of both its volume and age. It lies at\na 35° bend in the edge of the Gulf of California rift system, at a location where the character\nof the Gulf extensional province, in terms of topography, style of faulting, and\npaleomagnetic rotations, changes dramatically along strike.\nThis chapter presents a speculative model linking the along-strike structural variations\nof the extensional province at this location, and the two major episodes of volcanism\nin the Puertecitos Volcanic Province ca. 6 Ma and 3 Ma, to events in the\nevolution of the spreading and transform system nearby in the Gulf of California. Two\nfracture zone systems project northwestward into the Puertecitos Volcanic Province.\nThe Guaymas transform fault system passes through the Ballenas Channel and is\naligned with the southern boundary of the volcanic province; the Tiburón fracture\nzone (between Isla Tiburón and Isla Angel de la Guarda) projects into the northcentral\npart of the province. The Tiburón fracture zone was important during the\nearly evolution of the Gulf of California. The Guaymas transform fault system was\nmuch shorter during the early evolution of the Gulf of California was only active near\nthe Puertecitos Volcanic Province after 2 Ma. The Tiburón fracture zone may have\nbeen connected to a west-northwest-trending zone of deformation on land, the\nMatomi accommodation zone. Regional field evidence suggests that this accommoda:\ntion zone was active in late Miocene time and may have localized most of the vents for\nthe voluminous ca. 6 Ma volcanism of the northern Puerteci tos Volcanic Province. An\nepisode of 3.3-2.7 Ma volcanism in the extending region is related to a Pliocene jump\nof one Gulf of California spreading center from the Tiburón basin into this area\n(which is now the lower Delfin basin). Continental extension, growth faulting, and\nbasin formation in Pliocene time in the southern part of the Puertecitos Volcanic\nProvince probably preceded this spreading center jump by 1 to 2 m.y.\nThe temporal and spatial aspects of extension in this model may explain the\nstructural transition seen in the Puertecitos region. North of the Puertecitos Volcanic\nProvince, the San Pedro Martir fault and basin and range topography partly reflect\npre-6 Ma extension. Regions to the south, from Puertecitos southward to Gonzaga\nBay, may have been unaffected by extension at this time. The pre-Pliocene rift margin\nprobably passed through the northeast part of the province and southeastward into\nthe Gulf of California, east of Isla Angel de la Guarda. When major deformation began to affect the main part of the volcanic province, the motion in the sector from\nPuertecitos to Gonzaga Bay may have been primarily transform in nature, producing\na very different structural style from that inherited from the earlier transtensional\nhistory in the region north of the Matomi accommodation zone.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44906, title ="Age and stratigraphic relationships of pre- and syn-rift volcanic deposits in the northern Puertecitos Volcanic Province, Baja California, Mexico", author = "Nagy, Elizabeth A. and Grove, Marty", journal = "Journal of Volcanology and Geothermal Research", volume = "93", number = "1-2", pages = "1-30", month = "November", year = "1999", doi = "10.1016/S0377-0273(99)00080-3", issn = "0377-0273", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140414-080523933", note = "© 1999 Elsevier Science B.V. Received 6 October 1997; accepted 20 August 1998. E.A.N. thanks M.A. House, A.J.R. Kent, C.J. Lewis, and X.Y. Quidelleur for helpful discussions and reviews of early versions of this manuscript. K. Holt, K. Rostedt, T. Tyndall, and K. Wertz are thanked for invaluable field assistance, and P. Kokelaar and M. Howells are thanked for their enlightening\nvisit to the field area. X.Y. Quidelleur and K.D. Mahon are also acknowledged for providing software employed to analyze the ^(40)Ar/^(39)Ar results. G. Axen is thanked for providing a preprint (Axen and Fletcher, 1998) and C.J. Lewis is thanked for providing assistance with Fig. 1. We appreciate helpful reviews by G. Axen, C. Devey, and M. Heizler. This work was supported by NSF grants EAR-9218381,\n-9296102, and -9614674. This is contribution 6220 from the Division of Geological and Planetary Sciences of the California Institute of Technology.", revision_no = "12", abstract = "Geologic mapping of volcanic strata of the northern Puertecitos Volcanic Province (PVP) in northeastern Baja California, Mexico, performed in conjunction with ^(40)Ar/^(39)Ar analysis and petrochemical study, documents the Miocene geologic history of a well-preserved volcanic succession within the northern Sierra Santa Isabel and its relationship to the evolving Pacific–North America plate boundary. Subduction-related volcanic deposits, well-exposed in profile along the northern margin of the PVP in the informally named Santa Isabel Wash region, span pre-17 to 15 Ma. Minor rift-related volcanism occurred at ∼12.5 and ∼9 Ma, prior to voluminous PVP-forming volcanism at ∼6–6.5 Ma. Isochron ages typically exhibit precision (1σ) for plagioclase of ±2–7% and for anorthoclase and sanidine of ±2–5%, and replicate analysis of an internal anorthoclase standard indicate ∼1–2% reproducibility within a given irradiation and ∼2.5% for samples irradiated separately. Improved local correlations made possible by the rich stratigraphic section preserved in Santa Isabel Wash help constrain the relationships of several widespread pyroclastic flow deposits in northeastern Baja California. These correlations are important for both paleomagnetic studies within the region and for establishing geologic ties across the Gulf of California. The combined mapping and age results imply that most extensional deformation in the study area is post-6 Ma, although some earlier faulting and the development of the pre-6 Ma Matomı́ accommodation zone are also documented. Results support a transitional plate boundary model which implies that much of the Pacific–North America relative plate motion north of Delfı́n basin (i.e., the northernmost Gulf of California) is accommodated on N- to NNW-striking faults developed during Late Miocene ENE-directed extension. The model predicts a zone of divergence east of the PVP which provides a structural mechanism for the positions and jumps of nearby Gulf of California spreading centers (Upper and Lower Tiburón and Delfı́n basins) since 6 Ma, and relates major pulses of PVP volcanism at ∼6 and ∼3 Ma to these offshore spreading center adjustments. Results also imply that most extensional deformation in Santa Isabel Wash is the result of incorporation of the PVP into the Gulf Extensional Province ∼2–3 Ma due to northwestward propagation of the Guaymas fracture zone. Rotational deformation north of the PVP may have begun contemporaneously with this adjustment along the Gulf Extensional Province rift margin.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44905, title ="The Tuff of San Felipe: an extensive middle Miocene pyroclastic flow deposit in Baja California, Mexico", author = "Stock, Joann M. and Lewis, Claudia J.", journal = "Journal of Volcanology and Geothermal Research", volume = "93", number = "1-2", pages = "53-74", month = "November", year = "1999", doi = "10.1016/S0377-0273(99)00079-7", issn = "0377-0273", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140414-073556126", note = "© 1999 Elsevier Science B.V. Received 6 October 1997; received in revised form 12 March 1999; accepted 3 May 1999. \nThis work was supported by NSF grants EAR-92-18381 and EAR-96-14674. California Institute of Technology, Division of Geological and Planetary Sciences, contribution 6219. We thank Kip Hodges for access to the MIT CLAIR facility for the argon analyses. XRF analyses were performed at the University\nof Massachusetts, Amherst. We thank Fred McDowell, Luca Ferrari, and Kozo Uto for very helpful reviews of an earlier version of the manuscript.", revision_no = "13", abstract = "We document the existence of a widespread Miocene ash-flow tuff sheet in northeastern Baja California, Mexico. The Tuff of San Felipe (new name) was erupted from a vent east of the Sierra San Felipe of NE Baja California at ca. 12.6 Ma. This is the only widespread middle Miocene pyroclastic flow deposit identified in northeastern Baja California. Its distinctive age and widespread distribution make it an important marker horizon for structural reconstruction of this part of the Gulf Extensional Province, which is on the Pacific plate. The vent position, near the modern Gulf of California coast, allows the possibility that exposures of the Tuff of San Felipe may be preserved east of the Gulf on the North America plate in Sonora, yielding a tie point for the past relative position of the two plates. This paper summarizes all known information including petrography, geochemistry, geochronology, paleomagnetics, geographic distribution, and field appearance of this important tuff. It is a densely welded, crystal-rich, lithic-lapilli pyroclastic flow deposit, with 5–15% alkali feldspar, and can be 180 m thick in some locations near the vent. The Tuff of San Felipe is >40 m thick up to 40 km SW of the vent and >10 m thick at least 25 km NNW of the vent. A minimum volume estimate for the deposit is 54 km^3. Some recent ^(40)Ar/^(39)Ar age determinations suggest that the tuff is about 12.6 Ma in age. In all locations studied, the Tuff of San Felipe has a unique, low-inclination, reversed magnetization, which may record a field transition or a geomagnetic excursion within reversed polarity subchron C5Ar.2r (12.401 to 12.678 Ma). This low-inclination magnetization, as well as the mineralogy and age, is key to correlating the tuff across the region, because deposits are highly disrupted by subsequent normal faulting and outcrops are sparse and discontinuous away from the vent. The documentation of these characteristics is important because the Tuff of San Felipe is a key structural marker for the subsequent development of the Pacific–North America plate boundary in the Gulf of California, and it will be important to identify this tuff in outcrops elsewhere on the Baja California Peninsula and on the North America plate in Sonora.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/34919, title ="Constraints on the proposed Marie Byrd Land-Bellingshausen Plate Boundary from seismic reflection data", author = "Heinemann, J. and Stock, J.", journal = "Journal of Geophysical Research B", volume = "104", number = "B11", pages = "25321-25330", month = "November", year = "1999", doi = "10.1029/1998JB900079 ", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20121016-104022644", note = "© 1999 American Geophysical Union.\n\nReceived 10 September 1997; accepted 29 September 1998.\n\nThis research was supported by NSF grants OPP-\n9317318 and OPP-9317872. We thank Bruce Luyendyk, Robert Bird, and Phillip Schmidt for constructive reviews that helped to improve the paper. We thank the personnel of the Nathaniel B. Palmer and of Antarctic Support Associates for their hard work to ensure the success of the data collection during these two cruises. Contribution 8532, Division of Geological and Planetary Sciences, California Institute of Technology.", revision_no = "23", abstract = "Single-channel and multichannel marine seismic data off the coast of West Antarctica collected during two Nathaniel B. Palmer cruises (NP92-8 and NP96-2) in the vicinity of 65°S to 71°S, 220°E to 250°E, reveal a NNW trending graben. We interpret this graben to be part of the paleodivergent plate boundary between the Marie Byrd Land and Bellingshausen plates. This graben coincides with a −520 nT magnetic anomaly to the NNW and a −720 nT anomaly to the SSE, as well as a 20 mGal negative gravity anomaly. Seismic profiles subparallel to the graben (22 km/Ma half-spreading rate) reveal greater seafloor roughness to the NE, where seafloor spreading was slower, than to the SW (27 km/Ma half-spreading rate). These data allow the position of the Marie Byrd Land-Bellingshausen plate boundary to be constrained more precisely than has previously been possible, with a trend of N17°W from 68.52°S, 233.65°E to 68.41°S, 233.56°E. The sediment-filled graben has normal separation of sedimentary layers varying from 740±30 m to 580±20 m imaged in seafloor of age A33y (74 Ma). ", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44959, title ="Evolution of the Australian-Antarctic discordance since Miocene time", author = "Marks, Karen M. and Stock, Joann M.", journal = "Journal of Geophysical Research B", volume = "104", number = "B3", pages = "4967-4981", month = "March", year = "1999", doi = "10.1029/1998JB900075", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140415-124308456", note = "© 1999 American Geophysical Union.\n\nManuscript Accepted: 21 Oct 1998; Manuscript Received: 22 Apr 1998.\n\nReviews from Dietmar Mueller, Donna Jurdy, and an anonymous referee improved this manuscript. We thank J. Zachariasen for working on the finite rotation parameters for Chron 6y, and Amotz Agnon and Mike Gurnis for helpful discussions. This project was partially supported by NSF grant EAR-9296102 to J. M. Stock. K. Quinn's participation was supported by the Summer Undergraduate Research Fellowship (SURF) program of the California Institute of Technology. Contribution 8535, California Institute of Technology, Division of Geological and Planetary Sciences. The magnetic anomaly identifications, finite rotation parameters, and images of the reconstructions are available on the Worldwide Web site http:// ibis.grdl.noaa.gov/SAT/kmm/aad.intro.html.", revision_no = "14", abstract = "In this study we chronicle the development of the Australian-Antarctic discordance (AAD), the crenelated portion of the Southeast Indian Ridge between ∼120° and 128°E, since anomaly 6y time (19 Ma). We reconstruct satellite-derived marine gravity fields and depth anomalies at selected times by first removing anomalies overlying seafloor younger than the selected age, and then rotating the remaining anomalies through improved finite rotations based on a very detailed set of magnetic anomaly identifications. Our gravity field reconstructions reveal that the overall length of the Australian-Antarctic plate boundary within the AAD has been increasing since 19 Ma. Concomitantly, the number of propagating rifts and fracture zones in the vicinity of the discordance has increased dramatically in recent times, effectively dividing it into its present-day configuration of five distinct spreading corridors (B1-B5) that are offset alternately to the north and south and exhibit varying degrees of asymmetric spreading. Our bathymetric reconstructions show that the regional, arcuate-shaped, negative depth anomaly (deeper than predicted by normal lithospheric cooling models) presently centered on the discordance began migrating westward before anomaly 5ad time (∼14.4 Ma), and that a localized depth anomaly low, which at time 5ad lay on the ridge axis in spreading corridor B5, has been split apart by subsequent seafloor spreading. The magnetic anomaly patterns suggest that the depth anomaly is not always associated with a particularly contorted plate boundary geometry. Although the plate boundary within the AAD has been getting progressively more crenelated with time, this effect shows little to no migration along the ridge axis since 19 Ma. Thus any geodynamic models of the evolution of the discordance must account for the following observations: (1) the crenelation of the plate boundary within the AAD has increased with time, (2) the center of the crenelated zone does not appear to have migrated along the ridge crest, and (3) both the depth anomaly and the isotopic boundary between Pacific and Indian mantle have been migrating westward along the ridge axis but at apparently different rates. We suggest that both along-axis migration of the depth anomaly and isotopic boundary, as well as temporal variation in the upwelling mantle material beneath the AAD, and local tectonic effects are required in order to explain these observations.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44904, title ="Late Miocene to Recent transtensional tectonics in the Sierra San Fermín, northeastern Baja California, Mexico", author = "Lewis, Claudia J. and Stock, Joann M.", journal = "Journal of Structural Geology", volume = "20", number = "8", pages = "1043-1063", month = "August", year = "1998", doi = "10.1016/S0191-8141(98)00038-8", issn = "0191-8141", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140414-071657302", note = "© 1998 Elsevier Science Ltd. Received 4 March 1997; accepted in revised form 31 March 1998. This research was partially supported by National Science Foundation grants EAR-89-04022 and EAR-92-18381 and a Presidential Young Investigator Award (EAR-90-58217/EAR-92-96102) to Joann M. Stock. Additional support was provided to Claudia Lewis by the Harvard University Department of Earth and Planetary Sciences Grants-in-Aid for Fieldwork. We thank John Gephart for his generosity in allowing us to use his computer program FMSI for inverting fault/slickenline data, Rick Allmendinger and Randy Marrett for use of FaultKin, and the Division of Earth and Planetary Sciences at the California Institute of Technology for many resources necessary for completion of this project. We are grateful to Josephine Burns, Cheryl Contopulos, Tim Johnson, Dan Reilly, Chris Small, and Susan Turbek for assistance in the field and\nto Mark Abolins, Gary Axen, Jeff Lee, Arturo Martín Barajas, Tim Melbourne, Elizabeth Nagy, Zeke Snow, and Leslie Sonder for many helpful discussions. We thank Richard Norris and two anonymous referees for constructive reviews which greatly improved the manuscript.", revision_no = "15", abstract = "Basins and ranges within part of the Gulf of California Extensional Province (Mexico) have experienced complex distributed deformation, including normal and strike-slip faulting and block rotations, linked to dextral shear at the Pacific–North America plate boundary. In the Sierra San Fermı́n and southern Sierra San Felipe (northeastern Baja California), normal faulting began between 12.5 and 6 Ma, although most extension occurred between about 6 and 3 Ma, strongly influencing thickness and distribution of ash-flow tuffs and sedimentary deposits. Extension is generally <10% in 6 Ma rocks and somewhat more in 12.5 Ma rocks. Inversion of kinematic data, interpreted together with published paleomagnetic data, suggests that the axis of least principal stress was oriented between W–E and SW–NE in late Miocene time. Our data indicate an important change in the amount of dextral shear, but not necessarily the least principal stress direction (WSW–ENE), at about 3 Ma. Structural constraints limit significant sinistral strike-slip faulting, conjugate to the dextral plate boundary, to the last ∼3 My. Progressive changes in the geometry of faulting through time are consistent with regional strain partitioning within the Pacific–North America plate boundary zone, and are predicted by physical and analytical models of oblique divergence as the orientation of the stretching vector α changes to lower and lower values.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/49959, title ="The tectonic history of the Tasman Sea: A puzzle with 13 pieces", author = "Gaina, Carmen and Müller, R. Dietmar", journal = "Journal of Geophysical Research B", volume = "103", number = "B6", pages = "12413-12433", month = "June", year = "1998", doi = "10.1029/98JB00386", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140923-145247866", note = "© 1998 by the American Geophysical Union. Received August 20, 1997; revised December 23, 1997; accepted January 27, 1998. \n\nPaper number 98JB00386.\n\nThe results presented here are part of a Ph.D. project sponsored by the Australian Geological Survey Organisation.\nThe first author acknowledges support from the Department \nof Geology and Geophysics, University of Sydney. We thank the Royal Australian Navy for making digital magnetic anomaly data collected by the HMAS Cook available to us. We benefited from some insightful discussions with and unbiased views (at the 95% confidence level) from Ted Chang and Richard Gordon while they were visiting Sydney University. For digitizing magnetic anomaly identifications we used a program developed by Anahita Tikku from the Scripps Institution of Oceanography. Most of the figures were drafted using the GMT software [Wessel and Smith,\n1991]. This work was partially supported by National Science\nFoundation grant OCE-9416779 to J. Stock. JYR acknowledges support from the Centre National de la Recherche Scientifique and from the French Ministry of Education during his stay in Sydney. Marine gravity data south of 72ºS supplied by Seymour Laxon, University College London, and Dave McAdoo, NOAA. Géosciences Azur contribution\n174.", revision_no = "13", abstract = "We present a new model for the tectonic evolution of the Tasman Sea based on dense satellite altimetry data and a new shipboard data set. We utilized a combined set of revised magnetic anomaly and fracture zone interpretations to calculate relative motions and their uncertainties between the Australian and the Lord Howe Rise plates from 73.6 Ma to 52 Ma when spreading ceased. From chron 31 (67.7 Ma) to chron 29 (64.0 Ma) the model implies, transpression between the Chesterfield and the Marion plateaus, followed by strike-slip motion. This transpression may have been responsible for the formation of the Capricorn Basin south of the Marion Plateau. Another major tectonic event took place at chron 27 (61.2 Ma), when a counterclockwise change in spreading direction occurred, contemporaneous with a similar event in the southwest Pacific Ocean. The early opening of the Tasman Sea cannot be modeled by a simple two-plate system because (1) rifting in this basin propagated from south to north in several stages and (2) several rifts failed. We identified 13 continental blocks which acted as microplates between 90 Ma and 64 Ma. Our model is constrained by tectonic lineaments visible in the gravity anomaly grid and interpreted as strike-slip faults, by magnetic anomaly, bathymetry and seismic data, and in case of the South Tasman Rise, by the age and affinity of dredged rocks. By combining all this information we derived finite rotations that describe the dispersal of these tectonic elements during the early opening of the Tasman Sea.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44903, title ="Pacific-North America Plate Tectonics of the Neogene\nSouthwestern United States: An Update", author = "Atwater, Tanya and Stock, Joann", journal = "International Geology Review", volume = "40", number = "5", pages = "375-402", month = "May", year = "1998", doi = "10.1080/00206819809465216", issn = "0020-6814", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140414-070221525", note = "© 1998 V. H. Winston & Son, Inc. Published online: 06 Jul 2010. We thank Brian Wernicke and J. Kent Snow for allowing us to use their results in advance of publication. We thank Gene Humphreys, John\nCrowell, Bruce Luyendyk, Craig Nicholson, Gary Axen, Michael Singer, and Marcy Davis for helpful reviews and Brian Wernicke, Doug Wilson, Gene Humphreys, Rob Twiss, Bob\nButler, Wayne Thatcher, and Peter Weigand for helpful conversations, advice, and suggestions. We thank the Hall Symposium participants for lively feedback and Gary Ernst for his reviews, advice, and patient good humor. This work was supported by NSF Grant EAR-9614674 to J. Stock. California Institute of Technology, Division of Geological and Planetary Sciences, Contribution No. 8534.", revision_no = "12", abstract = "We use updated rotations within the Pacific-Antarctica-Africa-North America plate circuit to calculate Pacific-North America plate reconstructions for times since chron 13 (33 Ma). The direction of motion of the Pacific plate relative to stable North America was fairly steady between chrons 13 and 4, and then changed and moved in a more northerly direction from chron 4 to the present (8 Ma to the present). No Pliocene changes in Pacific-North America plate motion are resolvable in these data, suggesting that Pliocene changes in deformation style along the boundary were not driven by changes in plate motion. However, the chron 4 change in Pacific-North America plate motion appears to correlate very closely to a change in direction of extension documented between the Sierra Nevada and the Colorado Plateau. Our best solution for the displacement with respect to stable North America of a point on the Pacific plate that is now near the Mendocino triple junction is that from 30 to 12 Ma the point was displaced along an azimuth of ∼N60°W at rate of ∼33 mm/yr; from 12 Ma to about 8 Ma the azimuth of displacement was about the same as previously, but the rate was faster (∼52 mm/yr); and since 8 Ma the point was displaced along an azimuth of N37°W at a rate of ∼52 mm/yr.\n\nWe compare plate-circuit reconstructions of the edge of the Pacific plate to continental deformation reconstructions of North American tectonic elements across the Basin and Range province and elsewhere in order to evaluate the relationship of this deformation to the plate motions. The oceanic displacements correspond remarkably well to the continental reconstructions where deformations of the latter have been quantified along a path across the Colorado Plateau and central California. They also supply strong constraints for the deformation budgets of regions to the north and south, in Cascadia and northern Mexico, respectively.\n\nWe examine slab-window formation and evolution in a detailed re-analysis of the spreading geometry of the post-Farallon microplates, from 28 to 19 Ma. Development of the slab window seems linked to early Miocene volcanism and deformation in the Mojave Desert, although detailed correlations await clarification of early Miocene reconstructions of the Tehachapi Mountains. We then trace the post-20 Ma motion of the Mendocino slab window edge beneath the Sierran-Great Valley block and find that it drifted steadily north, then stalled just north of Sutter Buttes at ∼4 Ma.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/49132, title ="Pacific-North America Plate Tectonics of the Neogene Southwestern United States: An Update", author = "Atwater, Tanya and Stock, Joann", journal = "International Geology Review", volume = "40", number = "5", pages = "375-402", month = "May", year = "1998", doi = "10.1080/00206819809465216", issn = "0020-6814", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140902-135954936", note = "© 1998 by V. H. Winston & Son, Inc.\n\nWe thank Brian Wernicke and J. Kent Snow\nfor allowing us to use their results in advance of\npublication. We thank Gene Humphreys, John\nCrowell, Bruce Luyendyk, Craig Nicholson,\nGary Axen, Michael Singer, and Marcy Davis\nfor helpful reviews and Brian Wernicke, Doug\nWilson, Gene Humphreys, Rob Twiss, Bob\nButler, Wayne Thatcher, and Peter Weigand for\nhelpful conversations, advice, and suggestions.\nWe thank the Hall Symposium participants for\nlively feedback and Gary Ernst for his reviews,\nadvice, and patient good humor. This work was\nsupported by NSF Grant EAR-9614674 to J.\nStock. California Institute of Technology, Division\nof Geological and Planetary Sciences, Contribution\nNo. 8534.", revision_no = "11", abstract = "We use updated rotations within the Pacific-Antarctica-Africa-North America plate circuit to calculate Pacific-North America plate reconstructions for times since chron 13 (33 Ma). The direction of motion of the Pacific plate relative to stable North America was fairly steady between chrons 13 and 4, and then changed and moved in a more northerly direction from chron 4 to the present (8 Ma to the present). No Pliocene changes in Pacific-North America plate motion are resolvable in these data, suggesting that Pliocene changes in deformation style along the boundary were not driven by changes in plate motion. However, the chron 4 change in Pacific-North America plate motion appears to correlate very closely to a change in direction of extension documented between the Sierra Nevada and the Colorado Plateau. Our best solution for the displacement with respect to stable North America of a point on the Pacific plate that is now near the Mendocino triple junction is that from 30 to 12 Ma the point was displaced along an azimuth of ∼N60°W at rate of ∼33 mm/yr; from 12 Ma to about 8 Ma the azimuth of displacement was about the same as previously, but the rate was faster (∼52 mm/yr); and since 8 Ma the point was displaced along an azimuth of N37°W at a rate of ∼52 mm/yr.\n\nWe compare plate-circuit reconstructions of the edge of the Pacific plate to continental deformation reconstructions of North American tectonic elements across the Basin and Range province and elsewhere in order to evaluate the relationship of this deformation to the plate motions. The oceanic displacements correspond remarkably well to the continental reconstructions where deformations of the latter have been quantified along a path across the Colorado Plateau and central California. They also supply strong constraints for the deformation budgets of regions to the north and south, in Cascadia and northern Mexico, respectively.\n\nWe examine slab-window formation and evolution in a detailed re-analysis of the spreading geometry of the post-Farallon microplates, from 28 to 19 Ma. Development of the slab window seems linked to early Miocene volcanism and deformation in the Mojave Desert, although detailed correlations await clarification of early Miocene reconstructions of the Tehachapi Mountains. We then trace the post-20 Ma motion of the Mendocino slab window edge beneath the Sierran-Great Valley block and find that it drifted steadily north, then stalled just north of Sutter Buttes at ∼4 Ma.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/50897, title ="New Constraints on Plate Tectonic Puzzle of the SW Pacific", author = "Cande, S. C. and Stock, J.", journal = "Eos", volume = "79", number = "7", pages = "81-82", month = "February", year = "1998", doi = "10.1029/98EO00053", issn = "0096-3941", url = "https://resolver.caltech.edu/CaltechAUTHORS:20141028-074046308", note = "© 1998 American Geophysical Union. Article first published online: 19 Oct 2006. \n\nWe thank the officers, crew, and scientific stall of the RIV Ewing and R/VIB Palmer for their dedicated efforts. This work was funded by NSF grants OPP93-l7872 and OCE94-16989\nto Scripps Institution of Oceanography and grants OPP93-7318 and OCE94-l6779 to Caltech.", revision_no = "11", abstract = "A long-standing problem in the tectonics of the southwest Pacific has been the lack of closure of the plate circuit linking the Antarctic, Australia, Lord Howe Rise, and Pacific plates in late Cretaceous and early Tertiary time [Molnar et al., 1975]. Avoiding unacceptable overlaps and underlaps in reconstructions of these plates requires invoking relative motion on one or more nebulous plate boundaries somewhere along the plate circuit, such as between East and West Antarctica, within West Antarctica [Stock and Molnar, 1987], or perhaps between the Lord Howe Rise and Challenger Plateau in the Tasman Sea [Lawver and Gahagan, 1994]. This problem is of more than mere local interest since the motion of the Pacific plate relative to the rest of the globe is constrained through its connection with West Antarctica.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44958, title ="Paleomagnetic evidence of localized vertical axis rotation during Neogene extension, Sierra San Fermín, northeastern Baja California, Mexico", author = "Lewis, Claudia J. and Stock, Joann M.", journal = "Journal of Geophysical Research B", volume = "103", number = "B2", pages = "2455-2470", month = "February", year = "1998", doi = "10.1029/97JB02673", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140415-123711983", note = "© 1998 American Geophysical Union.\n\nManuscript Accepted: 18 Sep 1997; Manuscript Received: 10 Mar 1997.\n\nThis research was partially supported by a\nNational Science Foundation grant (EAR-92-18381) and a Presidential Young Investigator Award (EAR-92-96102) to Joann M. Stock. Additional support was provided by the Harvard University Department of Earth and Planetary Sciences Grants-in-Aid for Fieldwork. We thank\nJoe Kirschvink for the use of his paleomagnetics laboratory and sampling equipment, John Holt for patient guidance in the field and the lab, and the Division of Geological and Planetary Sciences at the California Institute of Technology for many resources necessary for completion of this project. We are grateful to Mario Rebolledo Vieyra and Liz Warner Holt for assistance in the field and to John Holt, Tim Melbourne, Elizabeth Nagy, and Leslie Sonder for many helpful discussions.\nRevisions were done at the Universitat de Barcelona, funded in part by a Fulbright Fellowship to Lewis. We thank John Geissman, Jonathan Hagstrum, Mark Hudson, Bruce Luyendyk, Steve Sheriff, and Paul Umhoefer for careful reviews. This is California Institute of Technology Division of Geological and Planetary Sciences contribution 5615.", revision_no = "17", abstract = "Paleomagnetic data from Sierra San Fermín in the Gulf of California Extensional Province indicate that localized clockwise rotations about vertical axes occurred during Pliocene through Recent extension and dextral shear. Relative declination discordances in upper Miocene and Pliocene ash flow tuffs indicate a net clockwise rotation of 30° ± 16°. Clockwise rotation between 12.5 and 6 Ma is statistically insignificant (11° ± 17°). Structural observations and geochronological data suggest that rotations in this area began post-6 Ma, comprising uniform-sense block rotations (oblique divergence) associated with extension and dextral slip in the northwest striking boundary between the Pacific and North American plates. Northeast striking sinistral-slip faults and north striking normal faults accommodate distributed dextral shear in this area, allowing fault blocks to rotate in a clockwise sense. A model for oblique divergence predicts ∼21 km of shear in the direction of relative plate motion and ∼20% (∼7 km) ENE directed extension, perpendicular to the Main Gulf Escarpment. A broad region of northeastern Baja California may have undergone similar distributed shear. Two possible dynamic models may explain this shear. In one model, rotation accumulates above a deep, subhorizontal, basal shear zone. Rotating blocks may extend downward to a detachment beneath the extensional province, either a low-angle eastward continuation of the San Pedro Mártir fault or to a basal shear surface on top of a subducted remnant of the Farallon plate. Alternatively, distributed dextral shear may be the surface manifestation of a deep vertical shear zone linking transform faults in the northern gulf with dextral transpeninsular faults. In either case, shear may have transferred northward onto faults west of the San Andreas fault, contributing to late Miocene to Recent clockwise rotation of the Western Transverse Ranges. This shear is not accounted for in the 300 km of dextral slip computed from cross-gulf geologic tie points.", } @book_section {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44940, title ="Pacific North America plate tectonics of the Neogene southwestern United States: An update", author = "Atwater, Tanya and Stock, Joann", pages = "393-420", month = "January", year = "1998", isbn = "9780966586909", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140415-074340042", note = "© 1998 Bellwether Pub.\n\nWe thank Brian Wernicke and J. Kent Snow\nfor allowing us to use their results in advance of\npublication. We thank Gene Humphreys, John\nCrowell, Bruce Luyendyk, Craig Nicholson,\nGary Axen, Michael Singer, and Marcy Davis\nfor helpful reviews and Brian Wernicke, Doug\nWilson, Gene Humphreys, Rob Twiss, Bob\nButler, Wayne Thatcher, and Peter Weigand for\nhelpful conversations, advice, and suggestions.\nWe thank the Hall Symposium participants for\nlively feedback and Gary Ernst for his reviews,\nadvice, and patient good humor. This work was\nsupported by NSF Grant EAR-9614674 to J.\nStock. California Institute of Technology, Division\nof Geological and Planetary Sciences, Contribution\nNo. 8534.", revision_no = "14", abstract = "We use updated rotations within the Pacific-Antarctica-Africa-North America plate circuit\nto calculate Pacific-North America plate reconstructions for times since chron 13 (33 Ma). The\ndirection of motion of the Pacific plate relative to stable North America was fairly steady between\nchrons 13 and 4, and then changed and moved in a more northerly direction from chron 4 to the\npresent (8 Ma to the present). No Pliocene changes in Pacific-North America plate motion are\nresolvable in these data, suggesting that Pliocene changes in deformation style along the\nboundary were not driven by changes in plate motion. However, the chron 4 change in\nPacific-North America plate motion appears to correlate very closely to a change in direction of\nextension documented between the Sierra Nevada and the Colorado Plateau. Our best solution\nfor the displacement with respect to stable North America of a point on the Pacific plate that is\nnow near the Mendocino triple junction is that from 30 to 12 Ma the point was displaced along an\nazimuth of ~N60°W at rate of ~33 mm/yr; from 12 Ma to about 8 Ma the azimuth of\ndisplacement was about the same as previously, but the rate was faster (~52 mm/yr); and since 8\nMa the point was displaced along an azimuth of N37°W at a rate of ~52 mm/yr.\nWe compare plate-circuit reconstructions of the edge of the Pacific plate to continental\ndeformation reconstructions of North American tectonic elements across the Basin and Range\nprovince and elsewhere in order to evaluate the relationship of this deformation to the plate\nmotions. The oceanic displacements correspond remarkably well to the continental reconstructions where deformations of the latter have been quantified along a path across the Colorado\nPlateau and central California. They also supply strong constraints for the deformation budgets\nof regions to the north and south, in Cascadia and northern Mexico, respectively.\nWe examine slab-window formation and evolution in a detailed re-analysis of the spreading\ngeometry of the post-Farallon microplates, from 28 to 19 Ma: Development of the slab window\nseems linked to early Miocene volcanism and deformation in the Mojave Desert, although\ndetailed correlations await clarification of early Miocene reconstructions of the Tehachapi\nMountains. We then trace the post-20 Ma motion of the Mendocino slab window edge beneath\nthe Sierran-Great Valley block and find that it drifted steadily north, then stalled just north of\nSutter Buttes at ~4 Ma.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44894, title ="Early Tertiary gravity field reconstructions of the Southwest Pacific", author = "Marks, K. M. and Stock, J. M.", journal = "Earth and Planetary Science Letters", volume = "152", number = "1-4", pages = "267-274", month = "November", year = "1997", doi = "10.1016/S0012-821X(97)00139-8", issn = "0012-821X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140411-144331262", note = "© 1997 Elsevier Science B.V. Received 10 June 1997; accepted 12 August 1997. We thank David McAdoo and Seymour Laxon for providing us with both preliminary and final versions of their ERS-1 satellite marine gravity field w8x covering the Ross Sea and Southwest Pacific Ocean. We also thank Jeanne Hardebeck for providing her Tasman Sea finite rotation. Reviews from Rupert Sutherland, Steve Cande, and an anonymous referee improved this manuscript. J. Stock was supported by NSF grant OCE-9416779. Contribution 6215, California Institute of Technology, Division of Geological and Planetary Sciences. Images of these reconstructions are on the web at http:rribisrgrdl.noaa. govrSAT under KMM’s directory. [AC]", revision_no = "11", abstract = "The aim of our study is to chronicle the development of plate boundaries in the Southwest Pacific Ocean during the early Tertiary. This region has been the subject of numerous and often conflicting studies that have attempted to construct the history of plate motion and plate boundary evolution as the Australia and Pacific plates separated from Antarctica. Our novel approach entails reconstructing gravity fields from satellite altimeter gravity by first removing anomalies overlying seafloor younger than a selected age, and then rotating the remaining anomalies through appropriate finite rotations. Our reconstructions reveal: (1) an extensional plate boundary (the Iselin rift) existed between West and East Antarctica prior to A24 time; (2) the arrival of the Southeast Indian ridge (SEIR) at the Tasman ridge (prior to A24) led to the extinction of the Iselin rift as well as the conversion of the easternmost portion of the Tasman plate boundary (between the SEIR and the Iselin rift) into a transform fault on the Pacific–Antarctic ridge; and (3) an early (A24 or younger) inception of the Australia–Pacific plate boundary. Our scenario for the opening of the Southwest Pacific Ocean can explain the present-day gravity anomalies and magnetic isochrons observed in the northwest Ross Sea. We find that the East Antarctic seafloor northeast of the Iselin Bank was generated by spreading on the Tasman ridge prior to A24 time.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44954, title ="Using borehole breakouts to constrain the complete stress tensor: Results from the Sijan Deep Drilling Project and offshore Santa Maria Basin, California", author = "Zajac, Blair J. and Stock, Joann M.", journal = "Journal of Geophysical Research B", volume = "102", number = "B5", pages = "10083-10100", month = "May", year = "1997", doi = "10.1029/96JB03914", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140415-112237965", note = "© 1997 American Geophysical Union.\n\nManuscript Accepted: 11 Dec 1996; Manuscript Received: 5 Aug 1996.\n\nThe authors thank Julie Shemeta for providing a lot of help with this work, Jerry Lohr for releasing the Santa Maria data to us, and Torch Operating Company for allowing us to publish the data. We acknowledge Leonid Germanovich, Bezalel Haimson, and Pavel Peška for their constructive reviews of this paper. We also thank Wessel and Smith [1995] for creating the GMT plotting tools. This work was supported by the National Earthquake Hazards Reduction Program of the U.S. Geological Survey (USGS) and by NSF grant EAR-9296102 for J. M. Stock. Research was supported by the USGS, Department of the Interior, under USGS award 1434-93-G-2297.\nThe views and conclusions contained in this document are\nthose of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. government. Caltech Seismological Laboratory Contribution Number 5729.", revision_no = "14", abstract = "We use borehole breakouts in nonvertical drill holes to constrain the directions of the three principal stresses and their relative magnitudes. In this paper we start by modifying previously published breakout selection criteria to work with highly deviated borehole data. We present a forward modeling technique using genetic algorithms and a nongradient N-dimensional optimizer to find the best fitting stress state for a set of breakout data. The stress state is parameterized by three Euler angles and the stress state ratio ø. A technique is developed to determine the 95% confidence weighted misfit between a model and the data. We then map out the 95% misfit confidence limits on the best fitting stress state. This technique is applied to data published by Qian and Pedersen [1991]. Removing their constraint of a vertical principal stress direction reduces the misfit between the stress state and the breakout data. We find that the best fitting stress state they report with a vertical principal stress direction lies outside our 95% confidence limits. We also invert breakouts in the offshore Santa Maria Basin, California. These data show a \"thrust faulting\" stress state with the maximum principal stress,\nS_1, at N148.5°E plunging 31.5°. The 95% confidence range for the azimuth of S_1 ranges from N143.0°E to N198.1°E. The stress ratio ø was found to be 0.82l^1_(0.584).", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44933, title ="The geodetic signature of the M8.0 Oct. 9, 1995, Jalisco subduction earthquake", author = "Melbourne, T. and Carmichael, I.", journal = "Geophysical Research Letters", volume = "24", number = "6", pages = "715-718", month = "March", year = "1997", doi = "10.1029/97GL00370", issn = "0094-8276", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140414-135006071", note = "© 1997 American Geophysical Union. \n\nManuscript Accepted: 14 Jan 1997. Manuscript Received: 4 Oct 1996. Paper number 97GL0037. The data were collected with the indispensable help of Dawnika Blatter, Phillip Bonstin, Jaime Dominguez, and Gerardo Perez-Ramos. The data were inverted using GINV and DISL programs written by Shawn Larsen. We thank the GIPSY-OASIS development team at JPL for GPS data-processing help. Supported by NSF grant EAR-9527810. California Institute of Technology Seismological Laboratory contribution #5795. ", revision_no = "16", abstract = "The October, 1995 Mw 8.0 Jalisco subduction earthquake has provided a thorough geodetic observation of the coseismic subduction process. An 11 station regional GPS network located directly onshore of the rupture demonstrates consistent vertical subsidence verified by tide gauge data and southwest-directed extension, with measured displacements reaching 1 meter. Unusually shallow and non-uniform faulting is required to explain the displacements. We determine that up to 5 meters of slip occurred within the upper 15 km of the thrust fault zone and 2 meters possibly as shallow as 8 km, and that slip was likely distributed in two main patches. The paucity of continental sediments in this subduction zone could be responsible for the anomalously shallow faulting.", } @article {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/44951, title ="Compression directions in southern California (from Santa Barbara to Los Angeles Basin) obtained from borehole breakouts", author = "Wilde, Melita and Stock, Joann", journal = "Journal of Geophysical Research B", volume = "102", number = "B3", pages = "4969-4983", month = "March", year = "1997", doi = "10.1029/96JB03734", issn = "0148-0227", url = "https://resolver.caltech.edu/CaltechAUTHORS:20140415-093934915", note = "© 1997 American Geophysical Union. A\n\nPaper number 96JB03734. Received March 15, 1996; revised October 1, 1996; accepted November 27, 1996. Some data were graciously provided by J. Scott\nHornafius and Laird Thompson of Mobil Exploration & Producing U.S. This work was supported by the Southern California Earthquake Center via NSF grant EAR 89-20136. Contribution 5656 of the Caltech Seismological Laboratory. SCEC publication 320. The early phases of this research were supported by the U.S. Geological Survey (USGS),\nDepartment of the Interior, under USGS award 1434-93-G-2297. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government. We thank Colleen Barton and an anonymous reviewer for very helpful\nreviews. Further details of the observations presented in this paper can be accessed on the internet at http://www.scecdc.scec.org/stress.", revision_no = "21", abstract = "Borehole elongation in 71 drill holes was used to infer breakout orientation and directions of maximum horizontal principal stress S_H for six areas west of the San Andreas fault in southern California: Santa Barbara, Ojai, Central Ventura Basin, East Ventura Basin, West Los Angeles Basin, and East Los Angeles Basin. Breakouts were determined from analysis of oriented four-arm caliper data. The breakouts form at the position of the maximum compressive stress on the borehole wall; if the borehole is vertical and parallel to one of the principal stress directions, the breakouts will form parallel to the minimum horizontal principal stress S_h orthogonal to the maximum horizontal principal stress S_H. Observations from deviated boreholes permit some constraints on the relative magnitudes of the principal stresses. In most cases the data permit either a thrust faulting (S_v