The first chapter of this thesis documents a provenance study, in which orthoquartzite clasts deposited in the Miocene Sespe Formation are linked to the Mesoproterozoic Shinumo Quartzite. The Sespe Formation outcrops in the Santa Monica Mountains and the Santa Ana Mountains, both in California. The Shinumo Quartzite outcrops only in Grand Canyon. We determine that the Shinumo Quartzite can be distinguished from other sources that may feed the Sespe Formation through its unique combination of a moderate paleomagnetic inclination and 1.2, 1.4, and 1.7 Ga detrital zircon spectrum peaks. This provenance link places an important constraint on the drainage of a paleo-Colorado River from Grand Canyon during Miocene time.
The second and third chapters of this thesis are hinged upon a geologic mapping project on Isla Ángel de la Guarda, a microcontinental block, in Baja California, Mexico. A plate reorganization at the end of the late Miocene andesitic arc marks the transfer of Baja California and the not-yet-rifted Isla Ángel de la Guarda to the Pacific plate from the North American plate. Between 3 and 2 Ma, the plate boundary jumped again, northward along the Ballenas Transform fault. In this Pliocene time, units mapped in this study were deposited.
The oldest units mapped are Miocene-Pliocene volcanic flows, for which we have no lower age constraint. The oldest volcanic flow dated is a Pliocene andesite lava (3.916 ± 0.088 Ma from 40Ar/39Ar). We map Miocene to Pliocene volcanic flows and Pliocene to Quaternary sedimentary units in two field areas. The sedimentary units are probably results of Pliocene rifting-related basin subsidence. Geochemical data from X-ray fluorescence indicate that lavas are compositionally similar to ~12 Ma arc-related rocks mapped in the Puertecitos Volcanic Province. In the southern field area, the sedimentary units are overlain by a Pliocene basaltic andesite with an 40Ar/39Ar age of 2.754 ± 0.021 Ma. We map several NNE-striking faults throughout both field areas, which cut NNW-striking bedding in Pliocene units. The Pliocene volcanic flows and sedimentary units were probably tilted before faulting, and the faults are likely linked to the Northern Salsipuedes Basin, offshore of the island in the Ballenas Channel. Both of these events may be results of 3-2 Ma rifting.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Stock, Joann M.}, } @phdthesis{10.7907/XTZX-X107, author = {Witkosky, Rebecca Amber}, title = {Tectonics in Nevada and Southern California: Subsidence of the Ediacaran Johnnie Formation, Cumulative Offset Along the Lavic Lake Fault, and Geomorphic Surface Development Along the Southern San Andreas Fault}, school = {California Institute of Technology}, year = {2019}, doi = {10.7907/XTZX-X107}, url = {https://resolver.caltech.edu/CaltechTHESIS:01172019-113222535}, abstract = {While we know the ages and tectonic histories of many critical geologic events in the history of the Earth, there are still questions regarding the timing of key events and structures that have and continue to influence life on this planet. This thesis includes three separate studies in Nevada and southern California: two potential new methods for measuring/organizing geologic time, and also an analysis of the long-term displacement along an active fault in the eastern California shear zone. In Chapter II, we used tectonic subsidence modeling to find that the Shuram carbon isotopic excursion in the Ediacaran Johnnie Formation likely occurred from 585-579 Ma, and that incision of the Rainstorm Member shelf occurred during the 579 Ma Gaskiers glaciation. The pre-Shuram-excursion chemostratigraphic carbon isotope profiles from the Khufai Formation in Oman and the type locality of the Johnnie Formation in Nevada are both generally positive and therefore possibly correlative. In Chapter III, we determined the cumulative tectonic offset along the Lavic Lake fault, an active structure that ruptured with >5 m of coseismic slip in the 1999 Mw 7.1 Hector Mine earthquake. We calculated a net slip of 960 +70/-40 m, based on the slip vector formed by a vertically separated lithologic contact and a horizontally separated older cross fault. The net slip we calculated is significantly less than a previous estimate that was based on an offset magnetic gradient, a disparity that may be explained by considering off-fault deformation, as well as the unknown depth and nature of the source of the magnetic contrast. In Chapter IV, we explored using a new method for the relative dating of Quaternary geomorphic surfaces, which is based on the positive correlation between increased spectral contrast in thermal hyperspectral airborne imagery and surface age. With field data, we found that desert varnish scores, desert pavement scores, and vegetation spacing estimates also correlate positively with surface age, implying that these factors could contribute to the increased spectral contrast in airborne remote sensing spectra. Additionally, the general increase in the band depth of airborne spectra at 9.16 μm could be due to increasing clay mineral abundance in progressively heavier desert varnish coatings on older surfaces. The positive correlation observed in this study between surface age and spectral contrast in airborne spectra can perhaps be used to develop a method for relative dating of varnished geomorphic surfaces elsewhere. All of the chapters in this thesis are broadly related by the concepts of geologic time and tectonic activity, which are two aspects of modern geology that are intrinsic to the science as a whole.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Stock, Joann M. and Wernicke, Brian P.}, } @phdthesis{10.7907/G94S-Z109, author = {Skinner, Steven Michael}, title = {Plate Tectonic Constraints on Flat Subduction and Paleomagnetic Constraints on Rifting}, school = {California Institute of Technology}, year = {2013}, doi = {10.7907/G94S-Z109}, url = {https://resolver.caltech.edu/CaltechTHESIS:06062013-151342444}, abstract = {Plate tectonics shapes our dynamic planet through the creation and destruction of lithosphere. This work focuses on increasing our understanding of the processes at convergent and divergent boundaries through geologic and geophysical observations at modern plate boundaries. Recent work had shown that the subducting slab in central Mexico is most likely the flattest on Earth, yet there was no consensus about what caused it to originate. The first chapter of this thesis sets out to systematically test all previously proposed mechanisms for slab flattening on the Mexican case. What we have discovered is that there is only one model for which we can find no contradictory evidence. The lack of applicability of the standard mechanisms used to explain flat subduction in the Mexican example led us to question their applications globally. The second chapter expands the search for a cause of flat subduction, in both space and time. We focus on the historical record of flat slabs in South America and look for a correlation between the shallowing and steepening of slab segments with relation to the inferred thickness of the subducting oceanic crust. Using plate reconstructions and the assumption that a crustal anomaly formed on a spreading ridge will produce two conjugate features, we recreate the history of subduction along the South American margin and find that there is no correlation between the subduction of a bathymetric highs and shallow subduction. These studies have proven that a subducting crustal anomaly is neither a sufficient or necessary condition of flat slab subduction. The final chapter in this thesis looks at the divergent plate boundary in the Gulf of California. Through geologic reconnaissance mapping and an intensive paleomagnetic sampling campaign, we try to constrain the location and orientation of a widespread volcanic marker unit, the Tuff of San Felipe. Although the resolution of the applied magnetic susceptibility technique proved inadequate to contain the direction of the pyroclastic flow with high precision, we have been able to detect the tectonic rotation of coherent blocks as well as rotation within blocks.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Clayton, Robert W. and Stock, Joann M.}, } @phdthesis{10.7907/078P-0C05, author = {Selvans, Michelle Marie}, title = {Geophysical Investigations of Near-Surface Structure on the Earth and Mars}, school = {California Institute of Technology}, year = {2011}, doi = {10.7907/078P-0C05}, url = {https://resolver.caltech.edu/CaltechTHESIS:05252011-161906788}, abstract = {I use remote sensing and active seismic methods to investigate near-surface structure on the Earth and Mars. These studies provide insight into styles of crustal deformation acting on continental margins in regions of extension, as well as paleoclimates that shaped the polar ice caps on Mars. I map the overall structure of the ice-rich Planum Boreum deposit at the north pole of Mars using 178 orbits of Mars Advanced Radar for Subsurface and Ionosphere Sounding data, and find no deflection of the lithosphere beneath the ice load. Bright, laterally extensive subsurface reflectors in the radargrams define the surface underlying Planum Boreum, as well as the interface between the two main units, the stratigraphically older Basal Unit and the stratigraphically younger North Polar Layered Deposits. The volumes of these units, and the overall edifice, are determined to the greatest accuracy possible to date. On Earth, I use a GPS campaign network in the state of Jalisco to investigate tectonic motion and interseismic deformation in the area. The consistent magnitude and direction of station velocities on the Jalisco Block suggest that it is moving rigidly with respect to North America. We constrain extension across the bounding fault zones of the block to values that are slow compared to relative rates of motion at nearby plate boundaries. I study another continental rift zone, in the Ross Sea, Antarctica, with refraction seismic data collected during research cruise NBP0701. I construct velocity models from 71 sonobuoys that detect deep structure in the oceanic crust of the Adare Basin and the crust of the Northern Basin, which lies to the south on the continental shelf. We demonstrate the importance of using multi-channel seismic data to correct for ocean currents and changes in ship navigation, the finite-difference modeling techniques necessary for accurately determining 1D velocity profiles for each sonobuoy, and for tying true velocities to the multi-channel seismic images of subsurface structure. We construct 2D velocity profiles using widely spaced sonobuoys in the Adare Basin, and using overlapping sonobuoys along some lines in both basins, and across the shelf break, to investigate crustal structure in the region. Detection of the Moho at 5.5 km below the seafloor by one sonobuoy suggests relatively thin oceanic crust in the Adare Basin, and flat velocity contours across the margin suggest continuity in crustal structure between the two basins.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Stock, Joann M.}, } @phdthesis{10.7907/MXQF-GY83, author = {Downey, Nathan John}, title = {Tectonic History of the Osbourn Spreading Center and Dynamic Subsidence of the Congo Basin}, school = {California Institute of Technology}, year = {2009}, doi = {10.7907/MXQF-GY83}, url = {https://resolver.caltech.edu/CaltechETD:etd-08282008-093820}, abstract = {This is a thesis in two parts. First is the presentation of a new technique by which it is possible to constrain tectonic models of oceanic regions which are devoid of magnetic reversal anomalies. I applied this technique to the Osbourn region of the Southwest Pacific and determined the tectonic history of the Cretaceous Osbourn spreading center. The results of this analysis showed that the Osbourn Trough, although an extinct spreading center, was not part of the Cretaceous Pacific-Phoenix spreading center. The second part of this thesis involves study of the cratonic Congo sedimentary basin. I created instantaneous dynamic models of the Congo basin that are strongly constrained by observation and which demonstrate that the most recent subsidence event of the basin has a mantle dynamic origin. These models constrain the density structure of the upper mantle beneath the Congo. In addition, I examined geologic data that constrain the time-dependent history of the Congo basin in an attempt to determine the subsidence mechanism of cratonic sedimentary basins.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Stock, Joann M.}, } @phdthesis{10.7907/DW9V-3831, author = {Dmochowski, Jane Ellen}, title = {Application of MODIS-ASTER (Master) Simulator Data to Geological Mapping of Young Volcanic Regions in Baja California, Mexico}, school = {California Institute of Technology}, year = {2005}, doi = {10.7907/DW9V-3831}, url = {https://resolver.caltech.edu/CaltechETD:etd-05262005-150027}, abstract = {Visible, near infrared, short-wave infrared, and thermal infrared multi-channel remote sensing data, MODIS-ASTER (MASTER), are used to extract geologic information from two volcanic regions in Baja California, Mexico: Tres Virgenes-La Reforma Volcanic Region and the volcanic island of Isla San Luis. The visible and near infrared and short-wave infrared data were atmospherically corrected and classified. The resulting classification roughly delineates surfaces that vary in their secondary minerals. Attempts to identify these minerals using ENVI’s Spectral Analyst(TM) were moderately successful.
The analysis of the thermal infrared data utilizes the shift to longer wavelengths in the Reststrahlen band as the mineralogy changes from felsic to mafic to translate the data into values of weight percent SiO2. The results indicate that the general approach tends to underestimate the weight percent SiO2 in the image. This discrepancy is removed with a “site calibration,” which provides good results in the calculated weight percent SiO2, with errors of a few percent. However, errors become larger with rugged topography or low solar angle at the time of image acquisition.
Analysis of bathymetric data around Isla San Luis, and consideration of the island’s alignment with the Ballenas transform fault zone to the south and volcanic seamounts nearby, suggest Isla San Luis is potentially volcanically active and could be the product of a “leaky” transform fault. The results from the image analysis in the Tres Virgenes-La Reforma Volcanic Region show the La Reforma and El Aguajito volcanic centers to be bimodal in composition and verify the most recent volcanism in the Tres Virgenes region to be basaltic-andesite. The results of fieldwork and image analysis indicate that the volcanic products of the central dome of La Reforma are likely a sequence of welded ash flow tuffs and lavas of varied composition, evidence of its origin as a caldera.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Stock, Joann M. and Clayton, Robert W.}, } @phdthesis{10.7907/VB6N-HC69, author = {Keller, William R.}, title = {Cenozoic Plate Tectonic Reconstructions and Plate Boundary Processes in the Southwest Pacific}, school = {California Institute of Technology}, year = {2005}, doi = {10.7907/VB6N-HC69}, url = {https://resolver.caltech.edu/CaltechETD:etd-01102005-223039}, abstract = {The Australia-Pacific-Antarctic plate circuit has long been a weak link in global plate reconstruction models for Cenozoic time. The time period spanning chron 20 to chron 7 (43-25 Ma) is particularly problematic for global plate models because seafloor spreading was occurring in two poorly constrained regions in the Southwest Pacific - the Macquarie Basin southwest of New Zealand, and the Adare Basin north of the Ross Sea, Antarctica. I present a new shipboard dataset collected aboard several recent geophysical cruises which places important constraints on the tectonic evolution of these two regions. Utilizing multibeam bathymetry, magnetic, gravity, and seismic data in the Macquarie Basin, I am able to locate tectonic features and magnetic anomalies with greater accuracy than was previously possible. These tectonic features and magnetic anomalies are then used to calculate relative motion between the Australia and Pacific Plates for chrons 18-11 (40-30 Ma). I use revised locations of the rifted margins along the boundary of the Macquarie Basin to determine a best-fit pre-rift reconstruction for this region. During this same time period, seafloor spreading between East and West Antarctica was occurring along the Adare Trough, an extinct spreading center located north of the Ross Sea. Motion along the Adare Trough accounts for roughly 180 km of previously unrecognized motion between East and West Antarctica. I present multibeam and seismic data in the Adare Basin that place constraints on the timing and character of motion along this plate boundary.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Clayton, Robert W. and Stock, Joann M.}, } @phdthesis{10.7907/8K9G-SS73, author = {Persaud, Patricia}, title = {Images of Early Continental Breakup in and around the Gulf of California and the Role of Basal Shear in Producing Wide Plate Boundaries}, school = {California Institute of Technology}, year = {2004}, doi = {10.7907/8K9G-SS73}, url = {https://resolver.caltech.edu/CaltechETD:etd-12032003-113513}, abstract = {Active faulting in the northern Gulf of California occurs over a broad zone, 70 x 200 km, affecting two-thirds of the width of new crust that has formed there starting at 6 Ma. This is an unusually wide plate boundary zone with a high density of faults and no evidence for the formation of normal oceanic crust. Over 3000 km of high-resolution, multichannel seismic data were used to map out this zone of distributed faulting and identify multiple basins within the broad rift zone. Previously, numerical models have shown that deformation shifts from one place to another by various mechanisms of strengthening of the active rift zone relative to adjacent regions. Models are presented here that for the first time, show the development of multiple active faults across the width of the plate boundary. These models do not rely on strengthening or weakening effects; rather they assume that shear at the base of the brittle crust is distributed and explore the effects of distributed shear on the style of deformation. Addiionally, the effect of obliquity on the style of deformation is studied and the styles of faulting produced in the models represent a wide range of geological structures, ranging from half-grabens to flower structures. The style of faulting in the northern Gulf of California is produced in a model with distributed shear using the published obliquity for this region.
One mechanism for distributing shear at the base of the brittle crust is lower crustal flow. If a significant amount of lower continental crust exists within the Gulf, it may have flowed in the past. A study of the crustal thickness variations in the continental margins of the Gulf is presented here, that shows thinner crust in a ~50 km wide zone close to the Gulf, along the entire eastern Baja California peninsula. This thinned crust is associated with the eastern Peninsular Ranges batholith. In contrast, the western part of the batholith has a fairly uniform thickness of 35-40 km. It is possible that at the time of breakup, the lower crust was still behaving ductilely and that some of the lower continental crust from the margins now exists within the Gulf.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Clayton, Robert W.}, } @phdthesis{10.7907/1HWM-JP59, author = {Niemi, Nathan Alan}, title = {Extensional Tectonics in the Basin and Range Province and the Geology of the Grapevine Mountains, Death Valley Region, California and Nevada}, school = {California Institute of Technology}, year = {2002}, doi = {10.7907/1HWM-JP59}, url = {https://resolver.caltech.edu/CaltechETD:etd-09122001-155631}, abstract = {Geologic mapping provides structural and stratigraphic observations which lead to new insights into the magnitude, timing, and rate of Cenozoic extensional tectonism in the Death Valley region of the Basin and Range province in the western United States. Detailed mapping of the Grapevine Mountains, in northeastern Death Valley, yields new information on the structural evolution of the Titus Canyon anticline, a west-vergent fold of the Cordilleran thrust belt. The Grapevine Mountains contain the longest exposure of west-vergent folding in the Death Valley region, and detailed mapping supports previous interpretation of this structure as a piece of a single, laterally continuous fold, whose extensionally dismembered fragments form a key marker in reconstructions of Basin and Range extension. Such an interpretation suggests >100 km of west-north-west translation of the Grapevine Mountains away from the Sheep Range in late Cenozoic time. Correlation and re-interpretation of Cenozoic sedimentary and volcanic strata between the Sheep Range and the Grapevine Mountains indicate that this extension occurred on two separate extensional systems, the Sheep Range detachment system, and the Northeastern Death Valley detachment system. The former was active from 16-14 Ma, while the latter was active from 12.5-8 Ma. In contrast, stratigraphic and sedimentological data from the Eagle Mountain Formation suggests that, although extension across the central Death Valley region accommodated a similar magnitude of extension as the northern Death Valley region, ~100 km, extension across this region occurred post-11 Ma, and largely between 8-6 Ma. New geodetic and paleoseismic data are also presented from the eastern Basin and Range. These data indicate that slow (~4 mm/yr), long term (100s ka) strain accumulation is accommodated, geologically, by short (1000s yr) periods of fast (>1cm/yr) strain release, suggesting that the appearance of diffuse deformation across the eastern Basin and Range is likely due to time-averaging of many temporally discrete high-strain release earthquake clusters. These observations together suggest that the diffuse nature of intra-continental extension in the Basin and Range province may be the result of the summation of many spatially and temporally distinct extensional events, which, when active, progress at very high rates}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Stock, Joann M.}, } @phdthesis{10.7907/W46E-ZY34, author = {Billen, Magali Isabelle}, title = {I. Seafloor Morphology of the Osbourn Trough and Kermadec Trench and II. Multiscale DynamiCS of Subduction Zones}, school = {California Institute of Technology}, year = {2002}, doi = {10.7907/W46E-ZY34}, url = {https://resolver.caltech.edu/CaltechETD:etd-11012001-142941}, abstract = {This thesis aims to demonstrate that integration of detailed observations of deformation at short to long length scales with carefully formulated numerical modeling is an effective method for simulating the complex multiscale nature of mantle-lithosphere dynamics. In Part I, marine geophysical observations are used to determine the origin of the Osbourn Trough, a long linear depression within the Pacific Plate seaward of the Tonga-Kermadec Trench, and to determine the elastic strength of the subducting plate within the Kermadec Trench. Based on the morphology of the seafloor from swath bathymetry mapping and modeling of magnetic data, we conclude that the Osbourn Trough is an extinct spreading center which stopped spreading about 72 million years ago. Swath bathymetry mapping within the Kermadec Trench reveals extensive faulting within the trench on the subducting plate, with oblique grabens aligned perpendicular to the absolute plate motion direction. Using isostatic flexural response methods, we find that the flexural rigidity (1e19-1e20 Nm) is smaller than normally found for old oceanic lithosphere reflecting a local reduction in the strength of the plate.
In Part II, regional 3-D dynamic models of the Tonga-Kermadec and Aleutian subduction zones are used to constrain lateral variations in viscosity in the upper mantle. Modeling of the dynamic topography of the overriding plate for the Tonga-Kermadec subduction zone requires a low viscosity and low density (-20 kg/m³) region within the wedge above the slab to decouple the slab-induced flow from. These efforts lead to a good fit to the observed shallow bathymetry on the overriding plate for a model with a slab density anomaly due to temperature of ~80 kg/m³. However, the geoid anomaly above the subduction zone is too large by 20-40 m at length scales of 100-1000 km. A reduction of the slab density by a factor of 1.5 is needed to match both the geoid and topography, suggesting the density anomaly of the slab due to temperature is compensated within the upper mantle (~100-300 km). Similar modeling for the Aleutians including a narrower low viscosity region and smaller density anomaly (-10 kg/m³) in the wedge is able to fit the geoid and topography without reducing the slab density.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Stock, Joann M. and Gurnis, Michael C.}, } @phdthesis{10.7907/4TQK-NH19, author = {Oskin, Michael Eugene}, title = {Part I. Tectonic Evolution of the Northern Gulf of California, Mexico, Deduced from Conjugate Rifted Margins of the Upper Delfín Basin. Part II. Active Folding and Seismic Hazard in Central Los Angeles, California}, school = {California Institute of Technology}, year = {2002}, doi = {10.7907/4TQK-NH19}, url = {https://resolver.caltech.edu/CaltechETD:etd-11252001-103911}, abstract = {Part I of this thesis addresses the tectonic evolution of the Pacific-North America plate boundary through northwest Mexico and its implications for rifting processes. Offset ignimbrites support 255±10 km of opening across the Upper Delfín basin of the northern Gulf of California. Additional deformation from the continental margins supports 296±17 km total plate boundary displacement between coastal Sonora and the Main Gulf Escarpment in Baja California, of which at least 276±13 km occurred since ~6 Ma. This strain history requires that the plate boundary localized into the the northern Gulf of California during latest Miocene time. Only a narrow width of upper continental crust foundered into the Upper Delfín basin, such that most of the crust between Isla Tiburón and Baja California must be new transitional oceanic crust and possibly lower continental crust contributed by inflow from the rift flanks. Extension of the margins of the Upper and Lower Delfín basins is <40% in most places, though the whole crustal column may have been thinned by a factor of two, further supporting that lower crustal flow has operated here. Opening of the Upper Delfín basin was accompanied by a steady or increased strain rate on its continental margins, contrary to the expected rheology of a narrow continental rift. Reevaluation of a critical deposit of marine rocks on Isla Tiburón indicates that initial marine incursion in the northern Gulf of California also occurred during latest Miocene time. Together, these records suggest that opening of the Upper Delfín basin was an abrupt event, accompanied by a localized zone of intense extension, marine incursion, and a rapid increase in strain rate. Continental rupture in the Upper Delfín basin does not appear to have been a response to crustal weakening by intracontinental extension, but rather may have resulted from a significant increase in strain rate, brought on by a change in boundary forces. Part II of this thesis develops methods to estimate seismic hazard from blind reverse faults by analysis of fault-related folding of Late Quaternary strata, with application to the Elysian Park anticline of Los Angeles, California.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Stock, Joann M. and Sieh, Kerry E.}, } @phdthesis{10.7907/Y9S0-0S33, author = {Eisner, Leo}, title = {A Reciprocity Method for Multiple Source Simulations}, school = {California Institute of Technology}, year = {2001}, doi = {10.7907/Y9S0-0S33}, url = {https://resolver.caltech.edu/CaltechETD:etd-08302001-030958}, abstract = {This thesis develops and applies the reciprocity method to assess the seismic site and path effects at a chosen location of interest. To do this, we show that the reciprocity theorem is valid for this application, and develop a technique to represent velocity models of sedimentary basins. Using these tools we test the accuracy of synthetic seismograms computed for southern California. Finally, we apply the reciprocity technique to evaluate the site and path effects for three selected sites in southern California.
The first chapter describes the reciprocity method for simulating seismograms due to multiple earthquake sources at a site of interest. It shows a theoretical proof of the method and discusses the practical implementation and accuracy for the finite difference technique. The numerical tests show that the reciprocal simulations can be performed with the same level of accuracy as the forward calculations.
The second chapter develops a new methodology to represent models of sedimentary basins with extremely low near surface velocities by replacing these velocities with equivalent medium parameters for a finite frequency signal. The new model has a higher minimum velocity, which makes the numerical simulations feasible, and minimizes the difference between the seismograms from the original and new model.
The third chapter validates the velocity model by comparing synthetics and data. It applies the reciprocity method and compares the full waveform synthetic seismograms with a large number of weak motion data. The discrepancies between the predicted waveforms and the data are interpreted by analyzing the attributes of seismograms to find regions of the model that are in error.
Finally the reciprocity technique is applied to calculate site and path effects in the Los Angeles area for three selected sites by simulating 75 source scenarios on 5 major southern California faults. The largest amplitudes at the selected sites are obtained from earthquakes on local faults rather than an earthquake on the San Andreas fault.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Stock, Joann M.}, } @phdthesis{10.7907/w8gc-n615, author = {Liu, Cangli}, title = {I. Rigid Body Penetration into Brittle Material. II. Phase Change Effect on Shock Wave Propagation}, school = {California Institute of Technology}, year = {1999}, doi = {10.7907/w8gc-n615}, url = {https://resolver.caltech.edu/CaltechTHESIS:04232013-084302487}, abstract = {Part I.
We have developed a technique for measuring the depth time history of rigid body penetration into brittle materials (hard rocks and concretes) under a deceleration of ~ 105 g. The technique includes bar-coded projectile, sabot-projectile separation, detection and recording systems. Because the technique can give very dense data on penetration depth time history, penetration velocity can be deduced. Error analysis shows that the technique has a small intrinsic error of ~ 3-4 % in time during penetration, and 0.3 to 0.7 mm in penetration depth. A series of 4140 steel projectile penetration into G-mixture mortar targets have been conducted using the Caltech 40 mm gas/ powder gun in the velocity range of 100 to 500 m/s.
We report, for the first time, the whole depth-time history of rigid body penetration into brittle materials (the G-mixture mortar) under 105 g deceleration. Based on the experimental results, including penetration depth time history, damage of recovered target and projectile materials and theoretical analysis, we find:
Part II.
Stress wave profiles in vitreous GeO2 were measured using piezoresistance gauges in the pressure range of 5 to 18 GPa under planar plate and spherical projectile impact. Experimental data show that the response of vitreous GeO2 to planar shock loading can be divided into three stages: (1) A ramp elastic precursor has peak amplitude of 4 GPa and peak particle velocity of 333 m/s. Wave velocity decreases from initial longitudinal elastic wave velocity of 3.5 km/s to 2.9 km/s at 4 GPa; (2) A ramp wave with amplitude of 2.11 GPa follows the precursor when peak loading pressure is 8.4 GPa. Wave velocity drops to the value below bulk wave velocity in this stage; (3) A shock wave achieving final shock state forms when peak pressure is > 6 GPa. The Hugoniot relation is D = 0.917 + 1.711u (km/s) using present data and the data of Jackson and Ahrens [1979] when shock wave pressure is between 6 and 40 GPa for ρ0 = 3.655 gj cm3 . Based on the present data, the phase change from 4-fold to 6-fold coordination of Ge+4 with O-2 in vitreous GeO2 occurs in the pressure range of 4 to 15 ± 1 GPa under planar shock loading. Comparison of the shock loading data for fused SiO2 to that on vitreous GeO2 demonstrates that transformation to the rutile structure in both media are similar. The Hugoniots of vitreous GeO2 and fused SiO2 are found to coincide approximately if pressure in fused SiO2 is scaled by the ratio of fused SiO2to vitreous GeO2 density. This result, as well as the same structure, provides the basis for considering vitreous Ge02 as an analogous material to fused SiO2 under shock loading. Experimental results from the spherical projectile impact demonstrate: (1) The supported elastic shock in fused SiO2 decays less rapidly than a linear elastic wave when elastic wave stress amplitude is higher than 4 GPa. The supported elastic shock in vitreous GeO2 decays faster than a linear elastic wave; (2) In vitreous GeO2 , unsupported shock waves decays with peak pressure in the phase transition range (4-15 GPa) with propagation distance, x, as α 1/x-3.35 , close to the prediction of Chen et al. [1998]. Based on a simple analysis on spherical wave propagation, we find that the different decay rates of a spherical elastic wave in fused SiO2 and vitreous GeO2 is predictable on the base of the compressibility variation with stress under one-dimensional strain condition in the two materials.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Ahrens, Thomas J. and Stock, Joann M.}, } @phdthesis{10.7907/S3V0-3M43, author = {Zajac, Blair J.}, title = {The State of Stress as Inferred from Deviated Boreholes: Constraints on the Tectonics of Offshore Central California and Cook Inlet, Alaska}, school = {California Institute of Technology}, year = {1998}, doi = {10.7907/S3V0-3M43}, url = {https://resolver.caltech.edu/CaltechTHESIS:06072010-160325894}, abstract = {This thesis introduces a new method of constraining the vector directions of the three principal stresses and their relative magnitudes, by using borehole breakouts in non-vertical drill holes. Unlike older stress state measurements from breakouts, this work does not presume that one of the principal stresses is Vertical. This method has important uses in complicated three-dimensional structures, such as in the Los Angeles basin, and in oil drilling applications.
Chapter 1 discusses why knowledge of the three-dimensional stress tensor is relevant to today’s science and examines the applications of the stress state determination technique discussed herein. The history of previous work is also described.
In Chapter 2 I discuss the techniques of determining the stress tensor from borehole breakouts, examining the physics of borehole breakouts, the theory of the inversion technique used, and data processing issues. The theory and data processing issues are not discussed separately in this work, since data processing issues often prompted new theoretical techniques. I first examine the physics of borehole breakouts and how the orientation of breakouts on the borehole wall relates to the local stress field. A new borehole breakout selection scheme which takes into account highly non-vertical boreholes is then presented along with a discussion of the real world problems of data gathering, identification, and processing. Having selected a borehole breakout data set using the criteria, I invert for the best fitting stress state using a new technique combining genetic algorithms and non- differential function optimizers. Finally, I present a way in which 95% confidence limits can be placed on the resulting stress tensor.
With all of the technical and theoretical pieces in place, I now examine several different data sets. Chapter 3 examines a borehole breakout data set publish by Qian and Pedersen [1991] from the Siljan Deep Drilling Project in Sweden and demonstrates that even for simple borehole breakout data sets, the stress state inversions assuming a vertical principal stress direction may fall outside of the 95% confidence limits of an inversion allowing non-vertical principal stress directions. My technique of displaying the borehole breakout data makes the data quality more obvious as compared to the way Qian and Pedersen [1991] plotted the data.
Chapter 4 examines a borehole breakout data set from the offshore Santa Maria Basin, California. This analysis presents vertical borehole breakout data that represent a maximum horizontal principal stress direction of N7°E, roughly consistent with other earthquake focal mechanism, GPS, and borehole breakout studies in the area. However, the stress state inversion of breakouts identified in the vertical and a limited number of nearly horizontal boreholes suggests a stress state very different from any other stress state results. This could imply that the three dimensional stress in the Santa Maria Basin is very complicated. However, given the limited amount of borehole breakouts identified in nearly horizontal wells, the stress state results from this data set are inconclusive.
Chapter 5 examines the largest data set used in this study, from a series of oil wells in Cook Inlet, Alaska. These are borehole caliper arm data from 21 different wells reaching a maximum deviation of 54° and 3,223 m true vertical depth. Stress state inversions of 31 different subsets of the borehole breakout data were performed. Inversion of breakouts identified in the top two of three marker beds analyzed in wells drilled from the Baker platform identified nearly degenerate thrust faulting stress states with the maximum principal stress axis, S_1, oriented horizontally WNWESE, perpendicular to the NNE-trending anticlinal structures. The stress state from the deepest marker is also a nearly degenerate thrust faulting stress state with S_1 oriented NNW—SSE, aligned with the regional direction of relative plate motion between the North American and Pacific plates. In between the shallow and deep stress state is an apparent normal faulting stress state with S_2 oriented subhorizontally ENE—WSW. This clockwise rotation of the stress tensor as a function of depth suggests that the stress field changes with depth, from a shallow stress state responsible for the local NNE-trending structures to a deeper one from the North American and Pacific plates’ collision zone. The observed normal faulting stress state between the two thrust faulting stress states is anomalous and may represent some sort of transition from the shallow to the deep stress state. Stress state profiles in 500 m true vertical depth (TVD) intervals show consistently oriented thrust faulting stress regimes with NNW—SSE trending S_1 azimuths. The thrust faulting S_3 principal stress direction is consistently within 30° of vertical, suggesting that while the assumption of a purely vertical principal stress direction is not valid, the stress tensor does not significantly rotate away from the surface conditions that require a purely vertical stress tensor. The nearly degenerate thrust faulting stress states determined from the Granite Point and the 10.8 km distant Baker platform breakouts are nearly identical, implying that the technique of using deviated borehole breakouts to invert for the regional stress is valid. The orientations of the maximum horizontal stress determined from the Cook Inlet borehole breakouts are consistent with other stress indicators in south-central Alaska and consistent with the direction of relative plate motion between the North American Plate and the Pacific plate. The S_1 axis for the Cook Inlet field trends due south plunging 3°. The 95% confidence limits allow the S_1 azimuth to vary from N156°E to N195°E and the plunge to vary from 10° to -4°. This stress state does not appear representative of the stress field for each subset of breakouts. The Granite Point S1 axis trends N19°W plunging 3°; the 95% confidence limits allow the azimuth to vary from N42°W to N7°E and the plunge to vary from 1° to 6°. The Baker platform S_1 axis trends N170°E plunging 8°; the 95% confidence limits on S_1 allow its azimuth to vary from N139°E to N191°E and its plunge to vary from 1° to 15°. Finally, the Dillon platform S_1 axis trends N69°W plunging 2°; the 95% confidence limits constrain the S_1 azimuth from N268°E to N324°E and the plunge from 8° to -4°. The more westerly orientation of S_1 at the Dillon platform may be related to the local NNE-trending anticlinal structures in the Cook Inlet Basin.
Chapter 6 concludes and summarized the results and conclusions from the thesis.
The first appendix contains in minute detail some of the mathematics describing the boreholes, breakouts, and coordinate system rotations used to perform this work. The second appendix contains the individual discussion and plots of the raw dipmeter data from all of the Cook Inlet, Alaska wells.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Stock, Joann M.}, } @phdthesis{10.7907/znpy-3311, author = {Nagy, Elizabeth Ann}, title = {Extensional Deformation and Volcanism Within the Northern Puertecitos Volcanic Province, Sierra Santa Isabel, Baja California, Mexico}, school = {California Institute of Technology}, year = {1997}, doi = {10.7907/znpy-3311}, url = {https://resolver.caltech.edu/CaltechTHESIS:01132010-093747416}, abstract = {Geologic features at the western edge of the Gulf Extensional Province (GEP) in northeastern Baja California, Mexico, record details of Pacific-North American (PAC-NAM) plate boundary history prior to and during its establishment within the Gulf of California. Methods of study in Santa Isabel Wash (SIW) (informally named) in the northern Sierra Santa Isabel include geologic mapping of ~140 km^2 (1:20000 scale) along the northern margin of the Miocene-Pliocene Puertecitos Volcanic Province (PVP), (40)Ar/(39)Ar geochronology, electron microprobe analysis, paleomagnetic study, and petrography. Local Neogene stratigraphy (spanning ~17-6 Ma) includes volcaniclastic breccias, basaltic to dacitic lava flows, and rhyolitic pyroclastic flow deposits. The completeness of the lithologic package improves stratigraphic correlations between the PVP and nearby regions.
High-angle extension-related faults cut all rocks in SIW. The southeastward projection of the pre-6 Ma Matorni accommodation zone, which separates a northern region of greater and more prolonged extension from a less extended southern zone, may pass on the north side of SIW. Paleomagnetic analysis indicates no vertical axis rotations in SIW since 6 Ma. This contrasts with regions north of the Matomi accommodation zone where clockwise rotation has accompanied extensional deformation since 3-6 Ma. About 500 meters of post-6 Ma, E-side-down displacement occurs across two major, NNW-striking normal faults on the west side of SIW. These, and smaller synthetic and antithetic faults in the hanging walls, accommodate up to 4% E- to ENE-directed extension. Quaternary deformation is also documented.
A new model developed to explain ENE-directed extension in northeastern Baja California partitions present-day PAC-NAM plate motion between NNW-striking, sinistral dip-slip faults and N- to NNW-striking, dextral (oblique?) strike-slip fault(s) in the northernmost Gulf of California. The model offers explanations for the geometry of plate motion accommodation between the latitudes of the Agua Blanca fault and the PVP, bathymetric features near Wagner and Consag basins, the position and jumps of nearby spreading centers since 6 Ma, the greater width and bend in coastline of the northernmost Gulf of California, the incorporation of the PVP into the GEP 2-3 Ma, and suggests a transitional tectonic scenario between oceanic spreading centers and continental transforms (“Wagner Transition Zone”).
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Stock, Joann M.}, }