Updated mapping of active fault traces along the Calaveras Fault from high resolution 3DEP topography

Celina Driver, Madeline F. Schwarz, Malinda G. Zuckerman, Ramon Arrowsmith, Chelsea P. Scott, & Austin J. Elliott

Published September 8, 2024, SCEC Contribution #13932, 2024 SCEC Annual Meeting Poster #105

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 use new high resolution 1m/pix topography from the USGS 3D Elevation Mapping Program (3DEP) 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 zonehazard.

We mapped the CF in the Morgan Hill-Gilroy-Hollister area southeast of the San Francisco Bay Area from northwest of Coyote Lake to Paicines. We referenced satellite imagery and existing geological maps in addition to shaded-relief and slope maps. 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.

We present detailed maps of fault traces and geomorphic features along an entire 50 kilometers of the CF. Three mappers completed targeted mapping around Coyote Lake, San Felipe Lake, and Swanson Bluff. We observed differences in fault trace location, confidence, and continuity between the mappers. While all mappers located primary faults similarly, some mappers identified more secondary fault traces. The undergraduate mapper tended to assign traces with lower confidence, whereas the graduate level mappers assigned higher confidences. 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.

Key Words
fault zone mapping, Calaveras fault

Citation
Driver, C., Schwarz, M. F., Zuckerman, M. G., Arrowsmith, R., Scott, C. P., & Elliott, A. J. (2024, 09). Updated mapping of active fault traces along the Calaveras Fault from high resolution 3DEP topography. Poster Presentation at 2024 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Geology