SCEC Award Number 24084 View PDF
Proposal Category Individual Research Project (Single Investigator / Institution)
Proposal Title Mapping active fault traces at the transition from the localized San Andreas Creeping Section to distributed faulting in the southern San Francisco Bay area (Calaveras Fault)
Investigator(s)
Name Organization
Ramon Arrowsmith Arizona State University
SCEC Milestones A1-2, A1-3 SCEC Groups Geology, CCB, PBS
Report Due Date 03/15/2025 Date Report Submitted 03/22/2025
Project Abstract
 Active faulting along the Calaveras Fault (CF) including aseismic creep and moderate to large earthquakes poses seismic hazard to the southern San Francisco Bay Area. Existing fault maps, created before the acquisition of high resolution topographic data, coarsely characterize the CF in the US Geological Survey (USGS) Quaternary Fault and Fold Database (QFaults). We used new high resolution 1m/pix topography from the USGS 3D Elevation Mapping Program (3DEP) along with satellite imagery and existing geological maps to map the locations of active fault traces. These finer scale maps contribute to improved understanding of fault zone structure, fault behavior, and evaluation of fault zone hazard. We mapped the CF in the Morgan Hill-Gilroy-Hollister area southeast of the San Francisco Bay Area from northwest of Coyote Lake to southeast of Paicines. Three individuals with a range of experience with fault mapping (from senior undergraduate to graduate students) remotely mapped the fault zone at ~1:1500 scale using a systematized geomorphic mapping approach to determine fault trace location and confidence. Our resulting maps show greater fault trace discontinuity and geometric complexity along the fault zone compared to fault traces from QFaults and existing geological maps. Despite variations in confidence designations, all mappers observe two primary faults converging northward of Hollister and diverging into two strands around Coyote Lake in accordance with high relief and landsliding. These updated maps may be used by researchers and professionals for fault displacement hazard analysis and to examine landscape evolution along this active fault zone.
Intellectual Merit Mapping active faults provides a direct characterization of fault zone processes and their hazards. This project maps 50 km of the Calaveras Fault from Morgan Hill to southeast of Paicines, using newly available high-resolution topographic data to improve fault trace detail. The resulting maps reveal greater discontinuity and geometric complexity than previous work. Three mappers with varying experience remotely mapped at ~1:1500 scale using a standardized geomorphic approach to assess fault trace location and confidence. This offers a valuable epistemic characterization of fault mapping uncertainty and directly advances understanding of fault zone processes and hazards.
Broader Impacts This project has broader impacts resulting from the new map data as well as from the training and mentoring outcomes. The results of the fault mapping provide improved understanding for fault displacement hazards in this area with both urban and agricultural sectors. In addition, it supported an undergraduate who was mentored by two PhD students as well as senior faculty. The undergraduate gained valuable independent research experience and technical skills. The graduate students improved their mentoring skills. We also further systematized our fault mapping scheme which has applied value for industry and agency practice.
Project Participants Professor Ramon Arrowsmith along with Professor Chelsea Scott of ASU supervised the project. Malinda Zuckerman and Madeline Schwartz are ASU PhD students who mentored Celina Driver, an undergraduate at Oregon State University. We were loosely coordinated with Drs. Austin Elliott and Steve DeLong of the US Geological Survey.
Exemplary Figure See Figure 5. It compares line work showing the difference in experience. QFaults in purple. (Top row) Senior undergraduate, (Middle and bottom row) Graduate student. (D) Lower Coyote lake, (E) Landfill (F) Lower Hollister. This might be of broader interest to the SCEC community.
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