Dissertation/Thesis Abstract

A Multi-Method Assessment of Geophysical Methods to Locate Subsurface Active Faults in Hinkley Valley, Eastern California Shear Zone, California
by Jordan, Jaime Jonathan, M.S., California State University, Long Beach, 2019, 101; 13862076
Abstract (Summary)

Hinkley Valley, California is cut by multiple Quaternary active dextral faults including the Mt. General, Harper Lake, and Blackwater faults. These faults are associated with the Eastern California Shear Zone, a 100-km-wide band of discontinuous northwest-striking right-lateral strike-slip faults that collectively accommodate ~10–12 mm/yr of Pacific/ North American plate boundary deformation. Large sections of these faults are mapped as inferred, meaning that they lack surface expression and are buried by Quaternary alluvial fill. The proximity of these faults to communities and critical infrastructure pose considerable risk to the inhabitants of Southern California, where precise knowledge of fault locations is vital. This thesis summarizes the results of a two-phase geophysical study conducted to find the precise locations of the Blackwater, Mt. General and Harper Lake faults within Hinkley Valley. First, I conducted a 2-dimensional feasibility profile using gravity, magnetic, seismic refraction, conductivity profiling, and electrical resistivity methods over the Mt. General fault to assess which methods provide the most cost-effective and efficient approach to locate buried faults. I selected the potential-field methods of gravity and magnetic surveying for the expanded survey in Hinkley Valley due to their relative success in locating the fault and their efficient and inexpensive data collection procedures. Where there is a relatively shallow depth to bedrock (< 100 m), the Mt. General, Harper Lake, and Blackwater faults produce a measurable gravitational response that is corroborated by co-located magnetic anomalies. When the depth to bedrock is greater than 100 m, ambiguities in the subsurface prevent meaningful interpretation of the potential-field profiles without additional constraints. Combining the 2-D gravity and magnetic profiles with other geophysical observations reduce ambiguity in the data and constrain the projected fault locations with greater confidence. The general success of the applied geophysical methods in this study provides new insights and approaches to locating buried faults in the Eastern California Shear Zone.

Indexing (document details)
Advisor: Bormann, Jayne M.
Commitee: Francis, Robert D., Martin, Antony J.
School: California State University, Long Beach
Department: Geological Sciences
School Location: United States -- California
Source: MAI 81/1(E), Masters Abstracts International
Subjects: Geophysics
Keywords: Geophysical, Subsurface active faults, Hinkley Valley, Eastern California Shear Zone, California
Publication Number: 13862076
ISBN: 9781085574662
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