Investigating Crustal Deformation Associated With The North America-Pacific Plate Boundary In Southern California With GPS Geodesy

Persistent Link:
http://hdl.handle.net/10150/332879
Title:
Investigating Crustal Deformation Associated With The North America-Pacific Plate Boundary In Southern California With GPS Geodesy
Author:
Spinler, Joshua C.
Issue Date:
2014
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The three largest earthquakes in the last 25 years in southern California occurred on faults located adjacent to the southern San Andreas fault, with the M7.3 1992 Landers and M7.1 1999 Hector Mine earthquakes occurring in the eastern California shear zone (ECSZ) in the Mojave Desert, and the M7.2 2010 El Mayor-Cucapah earthquake occurring along the Laguna Salada fault in northern Baja California, Mexico. The locations of these events near to but not along the southern San Andreas fault (SSAF) is unusual in that the last major event on the SSAF occurred more than 300 years ago, with an estimated recurrence interval of 215± 25 years. The focus of this dissertation is to address the present-day deformation field along the North America-Pacific plate boundary in southern California and northern Baja California, through the analysis of GPS data, and elastic block and viscoelastic earthquake models to determine fault slip rates and rheological properties of the lithosphere in the plate boundary zone. We accomplish this in three separate studies. The first study looks at how strain is partitioned northwards along-strike from the southern San Andreas fault near the Salton Sea. We find that estimates for slip-rates on the southern San Andreas decrease from ~23 mm/yr in the south to ~8 mm/yr as the fault passes through San Gorgonio Pass to the northwest, while ~13-18 mm/yr of slip is partitioned onto NW-SE trending faults of the ECSZ where the Landers and Hector Mine earthquakes occurred. This speaks directly to San Andreas earthquake hazards, as a reduction in the slip rate would require greater time between events to build up enough slip deficit in order to generate a large magnitude earthquake. The second study focuses on inferring the rheological structure beneath the Salton Trough region. This is accomplished through analysis of postseismic deformation observed using a set of the GPS data collected before and after the 2010 El Mayor-Cucapah earthquake. By determining the slip-rates on each of the major crustal faults prior to the earthquake, we are able to model the pre-earthquake velocity field for comparison with velocities measured using sites constructed post-earthquake. We then determine how individual site velocities have changed in the 3 years following the earthquake, with implications for the rate at which the lower crust and upper mantle viscously relax through time. We find that the viscosity of the lower crust is at least an order of magnitude higher than that of the uppermost mantle, and hypothesize that this is due to mafic material emplaced at the base of the crust as the spreading center developed beneath the Salton Trough since about 6 Ma. The final study investigates crustal deformation and fault slip rates for faults in the northern Mojave and southern Walker Lane regions of the ECSZ. Previous geodetic studies estimated slip-rates roughly double those inferred via geological dating methods in this region for NW striking strike-slip faults, but significantly smaller than geologic estimates for the Garlock fault. Through construction of a detailed elastic block model, which selects only active fault structures, and applying a new, dense GPS velocity field in this region, we are able to estimate slip-rates for the strike-slip faults in the ECSZ that are much closer to those reported from geology.
Type:
text; Electronic Dissertation
Keywords:
Fault-slip rates; Postseismic deformation; San Andreas; Geosciences; Block model
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Geosciences
Degree Grantor:
University of Arizona
Advisor:
Bennett, Richard

Full metadata record

DC FieldValue Language
dc.language.isoen_USen
dc.titleInvestigating Crustal Deformation Associated With The North America-Pacific Plate Boundary In Southern California With GPS Geodesyen_US
dc.creatorSpinler, Joshua C.en_US
dc.contributor.authorSpinler, Joshua C.en_US
dc.date.issued2014-
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe three largest earthquakes in the last 25 years in southern California occurred on faults located adjacent to the southern San Andreas fault, with the M7.3 1992 Landers and M7.1 1999 Hector Mine earthquakes occurring in the eastern California shear zone (ECSZ) in the Mojave Desert, and the M7.2 2010 El Mayor-Cucapah earthquake occurring along the Laguna Salada fault in northern Baja California, Mexico. The locations of these events near to but not along the southern San Andreas fault (SSAF) is unusual in that the last major event on the SSAF occurred more than 300 years ago, with an estimated recurrence interval of 215± 25 years. The focus of this dissertation is to address the present-day deformation field along the North America-Pacific plate boundary in southern California and northern Baja California, through the analysis of GPS data, and elastic block and viscoelastic earthquake models to determine fault slip rates and rheological properties of the lithosphere in the plate boundary zone. We accomplish this in three separate studies. The first study looks at how strain is partitioned northwards along-strike from the southern San Andreas fault near the Salton Sea. We find that estimates for slip-rates on the southern San Andreas decrease from ~23 mm/yr in the south to ~8 mm/yr as the fault passes through San Gorgonio Pass to the northwest, while ~13-18 mm/yr of slip is partitioned onto NW-SE trending faults of the ECSZ where the Landers and Hector Mine earthquakes occurred. This speaks directly to San Andreas earthquake hazards, as a reduction in the slip rate would require greater time between events to build up enough slip deficit in order to generate a large magnitude earthquake. The second study focuses on inferring the rheological structure beneath the Salton Trough region. This is accomplished through analysis of postseismic deformation observed using a set of the GPS data collected before and after the 2010 El Mayor-Cucapah earthquake. By determining the slip-rates on each of the major crustal faults prior to the earthquake, we are able to model the pre-earthquake velocity field for comparison with velocities measured using sites constructed post-earthquake. We then determine how individual site velocities have changed in the 3 years following the earthquake, with implications for the rate at which the lower crust and upper mantle viscously relax through time. We find that the viscosity of the lower crust is at least an order of magnitude higher than that of the uppermost mantle, and hypothesize that this is due to mafic material emplaced at the base of the crust as the spreading center developed beneath the Salton Trough since about 6 Ma. The final study investigates crustal deformation and fault slip rates for faults in the northern Mojave and southern Walker Lane regions of the ECSZ. Previous geodetic studies estimated slip-rates roughly double those inferred via geological dating methods in this region for NW striking strike-slip faults, but significantly smaller than geologic estimates for the Garlock fault. Through construction of a detailed elastic block model, which selects only active fault structures, and applying a new, dense GPS velocity field in this region, we are able to estimate slip-rates for the strike-slip faults in the ECSZ that are much closer to those reported from geology.en_US
dc.typetexten
dc.typeElectronic Dissertationen
dc.subjectFault-slip ratesen_US
dc.subjectPostseismic deformationen_US
dc.subjectSan Andreasen_US
dc.subjectGeosciencesen_US
dc.subjectBlock modelen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineGeosciencesen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorBennett, Richarden_US
dc.contributor.committeememberBennett, Richarden_US
dc.contributor.committeememberRichardson, Randallen_US
dc.contributor.committeememberZandt, Georgeen_US
dc.contributor.committeememberJohnson, Royen_US
dc.contributor.committeememberFay, Noahen_US
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