@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", volume = "33", number = "1", pages = "403-426", month = "February", year = "2021", doi = "10.1111/bre.12473", issn = "0950-091X", url = "https://resolver.caltech.edu/CaltechAUTHORS:20200519-132017615", note = "© 2020 The Authors. Basin Research © 2020 John Wiley & Sons Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists. \n\nIssue Online: 22 January 2021; Version of Record online: 03 June 2020; Accepted manuscript online: 18 May 2020; Manuscript accepted: 29 April 2020; Manuscript revised: 22 April 2020; Manuscript received: 28 January 2020. \n\nResearch funding: National Science Foundation, USA. Grant Numbers: NSF‐OCE‐1654689, NSF‐OCE‐1654766.", revision_no = "11", 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/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 = "9", 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/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 = "14", 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).", }