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Author ORCID Identifier

https://orcid.org/0000-0001-8877-2176

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Geosciences

Year Degree Awarded

2019

Month Degree Awarded

September

First Advisor

Michele Cooke

Subject Categories

Geology

Abstract

Assessment of seismic hazards in southern California may be improved with more accurate characterization of active geometry, stress state, and slip rates along the active San Andreas fault strands within the San Gorgonio Pass region. For example, on-going debate centers on the activity and geometry of the Mill Creek and Mission Creek strands. Calculated misfits of model slip rates to geologic slip rates for six alternative active fault configuration models through the San Gorgonio Pass reveal two best-fitting models, both of which fit many but not all available geologic slip rates. Disagreement between the model and geologic slip rates indicate where the model fault geometry is kinematically incompatible with the interpreted geologic slip rate, suggesting that our current knowledge of the fault configuration and/or slip rates may be inaccurate.

Focal mechanism of microseismicity can estimate stress state; however, within the San Bernardino basin, some focal mechanisms show slip that is inconsistent with the interseismic strike-slip loading of the region. We show that deep creep along the nearby northern San Jacinto fault can account for this discrepancy. Consequently, if local stresses are estimated using these focal mechanisms, the resulting information about fault loading may be inaccurate. We also use another way to estimate the present-day, by calculating evolved fault tractions along a portion of the San Andreas fault using the time since last earthquake, fault stressing rates (which account for fault interaction), and co-seismic models of the impact of recent nearby earthquakes. Because this method considers the loading history of each fault, the evolved tractions differ significantly from the resolved regional tractions and can provide more accurate initial conditions for dynamic rupture models within regions of complex fault geometry.

Numerical models of restraining bends in a viscoelastic material have implications for how we model the Earth’s crust. Deforming the model at faster velocities decreases the amount of visco-relaxation, allowing the model to behave more elastically. Viscoelastic models allow for velocity-dependent deformation, which could improve our understanding of crustal deformation, especially within complex fault systems.

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