Author: Kimberly Diem Chi Blisniuk Publisher: ISBN: 9781267238320 Category : Languages : en Pages :
Book Description
Understanding the mechanics of plate boundaries and associated seismic hazards requires evaluation of how slip is distributed over Quaternary timescales along individual faults, across fault zones, and entire fault systems. Documenting such slip distributions over multiple time scales is challenging due to the difficultly of obtaining reliable ages for offset landforms. For instance, exposure ages from cosmogenic isotopes can be significantly affected by surface processes, and U-series dating of pedogenic carbonate provides only minimum ages because carbonate accumulation occurs after deposition. Fortunately, the controlling factors for the resulting age and age uncertainties of each method are relatively independent from each other, so a combination of cosmogenic isotope and U-series dating may significantly improve the reliability of landform dating and yield more reliable slip rate estimates. To understand how deformation is shared across the Pacific and North American plate boundary, a comprehensive slip rate history is presented at multiple locations and time-intervals from 6 sites across the paired Clark and Coyote Creek faults of the southern San Jacinto fault zone. Offsets are constrained from field mapping and high-resolution LiDAR topography data, and displaced alluvial fans were dated with U-series on pedogenic carbonate clast-rinds and/or in situ cosmogenic 10Be. In general, these results show that, in an arid setting where post-depositional processes are limited and multiple dating techniques can be applied, self-consistent landform ages may be obtained to yield reliable slip rate estimates. The results from this study show that (1) the rate of deformation across the southern San Jacinto fault zone has remained uniform and constant in time and space over at least the past 40 kyr, and probably since its early Quaternary initiation, (2) pronounced slip rate gradients exist along the length of both the Clark and Coyote Creek faults, declining from the northwest to the southeast, and (3) summed slip rates of ~13 to 17 mm/yr across the bedrock portion of southern San Jacinto fault zone suggests that since at least the latest Pleistocene, deformation across the Pacific-North America plate boundary has been partitioned fairly evenly between the southern San Andreas fault zone and San Jacinto fault zone.
Author: Publisher: Geological Society of America ISBN: 0813724759 Category : Science Languages : en Pages : 56
Book Description
"The San Jacinto right-lateral strike-slip fault zone is crucial for understanding plate-boundary dynamics, regional slip partitioning, and seismic hazards within the San Andreas fault system of southern California, yet its age of initiation and long-term average slip rate are controversial. This synthesis of prior and new detailed studies in the western Salton Trough documents initiation of structural segments of the San Jacinto fault zone at or slightly before the 1.07 Ma base of the Jaramillo subchron. In Special Paper 475, five new estimates of displacement are developed using offset successions of crystalline rocks; distinctive marker beds in the late Cenozoic basin fill; analysis of strike-slip-related fault-bend folds; quantification of strain in folds at the tips of dextral faults; and gravity, magnetic, and geomorphic data sets."--Publisher's website.
Author: Publisher: ISBN: Category : Geology Languages : en Pages : 304
Book Description
An overview of the history, geology, geomorphology, geophysics, and seismology of the most well known plate tectonic boundary in the world.
Author: David H. Forand Publisher: ISBN: Category : Languages : en Pages : 286
Book Description
Damage zones adjacent to or associated with faults are important to the geologic community because of their implications to hazards and their ability to preserve evidence for, and show history of, slip, fluid flow, and deformation associated with large strike-slip faults. We examine two fault zones in southern California where fault zone damage is expressed. We revisit the drilled crystalline core from the Cajon Pass California drill hole, 4 km northeast of the San Andreas fault (SAF), and 1 km north of the Cleghorn fault, to perform a systematic structural analysis of deformation and alteration associated with strike-slip faulting at the site. The core preserved 19 fault zones, 11 of which were not previously identified. The most significant fault is a fully intact steep-dipping fault zone at 3,402 m depth with potassium feldspar and epidote alteration. This fault correlates well with the nearby left-lateral Cleghorn fault. The extent of deformation varies within the core, and is controlled by the size of the fault zones intersected by the core. The extent of deformation varies and is controlled by the size of the faults the core intersected. We also examined the nature of right separation across the Clark fault damage zone along the Santa Rosa segment using a marker assemblage of biotite, hornblendebearing tonalite - marble - bearing metasedimentary rocks - migmatite located in Coyote Mountain and the southeast Santa Rosa Mountains. Separation measured from this study is 16.8 km + 3.67 km / -6.03 km. Our measurement uses the updated location of the Clark fault in Clark Lake Valley and matches a distinctive lithologic contact across the fault instead of matching the diffuse western boundary of the Eastern Peninsular mylonite zone as previously used. We calculate the errors associated with projecting the contacts across Quaternary cover to the trace of the Clark fault, and consider a range of projections. Additional strain may have been accommodated in folds and small faults within the damage zone of the San Jacinto fault zone. Two large map-scale folds deform the marker assemblage near the San Jacinto fault zone and we tested whether Cretaceous ductile deformation or brittle late Quaternary right slip produced the folds.
Author: Susanne U. Janecke Publisher: ISBN: 9780813724751 Category : Science Languages : en Pages : 60
Book Description
"The San Jacinto right-lateral strike-slip fault zone is crucial for understanding plate-boundary dynamics, regional slip partitioning, and seismic hazards within the San Andreas fault system of southern California, yet its age of initiation and long-term average slip rate are controversial. This synthesis of prior and new detailed studies in the western Salton Trough documents initiation of structural segments of the San Jacinto fault zone at or slightly before the 1.07 Ma base of the Jaramillo subchron. In Special Paper 475, five new estimates of displacement are developed using offset successions of crystalline rocks; distinctive marker beds in the late Cenozoic basin fill; analysis of strike-slip-related fault-bend folds; quantification of strain in folds at the tips of dextral faults; and gravity, magnetic, and geomorphic data sets."--Publisher's website.
Author: Justin W. Herbert Publisher: ISBN: Category : Languages : en Pages : 171
Book Description
This dissertation aims to understand fault system deformation using numerical models and analog experiments. In southern California, the southern Big Bend of the San Andreas fault (SAF) is a zone of transpression that accommodates deformation associated with the Pacific-North American plate boundary. Using three-dimensional boundary element method (BEM) models, I test the sensitivity of fault slip rates to a range of tectonic boundary conditions constrained by Global Positioning System (GPS) studies of the region (45-50 mm/yr and 320°- 325°). I have modified fault configurations derived from the Southern California Earthquake Center Community Fault Model of the San Gorgonio knot and the eastern California shear zone (ECSZ) to better represent the disconnected nature of active faults in southern California. The models with revised fault geometry produce slip rates that better match geologic strike-slip rates, thus validating the revisions. More northerly plate velocity (325°) produces greater transpression along the SAF system associated with greater uplift of the San Bernardino Mountains, greater reverse-slip rates along range bounding reverse thrust faults, lower strike-slip rates along the San Andreas and San Jacinto faults, and greater strike-slip rates along the eastern California shear zone (ECSZ) and Garlock fault. These results suggest that the degree of regional transpression controls the partitioning of deformation between uplift and slip along both the SAF system and the ECSZ. Along the San Bernardino strand of the SAF and across the ECSZ, geologic slip rates differ from those inverted from geodetic measurements, which may partly be due to inaccurate fault connectivity within geodetic models. I compare results from fault networks that follow mapped geologic traces and resemble those used in block model inversions, which connect the San Jacinto fault to the SAF near Cajon Pass and connect distinct faults within the ECSZ. The connection of the SAF with the San Jacinto fault decreases strike-slip rates along the SAF by up to 10% and increases strike-slip rates along the San Jacinto fault by up to 16%; however, slip rate changes are still within the large geologic ranges along the SAF. The insensitivity of modeled interseismic surface velocities near Cajon Pass to fault connection suggests that inverse models may utilize both an incorrect fault geometry and slip rate and still provide an excellent fit to interseismic geodetic data. Similarly, connection of faults within the ECSZ produces 36% greater cumulative strike-slip rates but less than 17% increase in interseismic velocity. Within the models that follow the mapped traces, off-fault deformation accounts for 40% ± 23% of the total strain across the ECSZ. This suggests that a significant portion of the discrepancy between the geologic and geodetically modeled slip rates in the ECSZ could be due to the geodetic inversion model assumption of zero permanent off-fault deformation. When using overconnected models to invert GPS for slip rates, the reduced off-fault deformation within the models can lead to overprediction of slip rates. Analog models of sandbox experiments performed at the Universite de Cergy-Pontoise (UCP) shed light on the amount of work required to create faults (Wgrow) in coarse sand. Casagrande shear experiments calculate a Wgrow that is consistent with that calculated in the sandbox and both values scale properly to crustal calculations. Calculations of Wgrow are higher for thicker sand pack layer experiments. Utilizing different materials within the compressional sandbox (GA39 sand and glass beads) shows the control of material properties on Wgrow as well. Numerical simulations of the UCP sandbox experiments test whether fault growth occurs via work minimization. To the first order, faults observed in sandbox experiments match the model predicted faults that minimize work in two-dimensional BEM simulations. The BEM models and work minimization shed light on fault growth path and timing.
Author: Drake Kerr (Graduate student) Publisher: ISBN: Category : Faults (Geology) Languages : en Pages : 0
Book Description
Abstract: Paleoseismic and geologic data on the southern San Andreas fault zone (SAFZ) show that there is a significant decrease in slip rate on the fault south of Cajon Pass. Transfer of slip from the SAFZ to the San Jacinto fault zone (SJFZ) near the northern terminus of the SJFZ is the likely cause of the decrease in slip rate, and paleoseismic data suggest some ruptures on the SAFZ have diverted down the SJFZ, rather than continuing on the SAFZ. A better understanding of the fault structure and activity on the northern SJFZ is needed to test these hypotheses. To understand where slip is transferred between the SAFZ and the SJFZ in the Cajon Pass, mapping of fault-related geomorphic features was conducted along the three major strands of the SJFZ between the northwestern end of the San Bernardino basin and the fault zone’s northwest termination in the San Gabriel Mountains. Field investigations were complemented by the use of LiDAR imagery to investigate the fault structure and geomorphology. In the San Gabriel Mountains, geomorphic evidence shows a smooth decrease in slip to the northwest. Consultant trench logs along the northern SJFZ reveal the middle strand had a surface rupture between years 1380 AD and 1810 AD. Whereas shallow trenching during this study on the Glen Helen strand of the SJFZ, which is closest to the SAFZ, revealed the last surface rupture occurred between 2960±105 and 1325±20 years ago. This result was unexpected as it was assumed that the Glen Helen strand closest to the SAFZ played a more prominent role in the interaction between the SAFZ and SJFZ. The paleoseismic data from the trenches, combined with the steady decrease in geomorphic evidence for Late Quaternary slip to the northwest on the SJFZ, and the decrease of SAFZ slip rate to the southeast suggest that slip is being transferred between the SAFZ and SJFZ over a zone of at least 20 km from the northwest extent of the SJFZ, southeast into the San Bernardino basin, and the middle strand of the SJFZ has the most active role in slip transfer.
Author: Kimberly Diem Chi Blisniuk
Author: 
Author: Geological Survey (U.S.).
Author: 
Author: Working Group on California Earthquake Probabilities
Author: David H. Forand
Author: Susanne U. Janecke
Author: Justin W. Herbert
Author: Drake Kerr (Graduate student)
Author: