DIGITAL COMPILATION OF CENTRAL AND NORTHERN CALAVERAS FAULT DATA FOR THE NORTHERN CALIFORNIA QUATERNARY FAULT MAP DATABASE: COLLABORATIVE RESEARCH WITH WILLIAM LETTIS & ASSOCIATES, INC. AND THE U.S. GEOLOGICAL SURVEY

The 146-km-long Calaveras fault plays a major role in accommodating plate-motion in the San Francisco Bay region, and is the primary conduit along which slip branches from the San Andreas fault in the southeastern Bay region. Prominent geomorphic expression of late Holocene surface traces along the entire length of the Calaveras fault, and a two hundred year seismicity record attest to its activity. Paleoseismic data, geodetic modeling and historical creep data suggest a present-day fault slip rate of about 14 +/- 5 mm/yr on the central section of the fault. Based on structural relations with other major faults, contemporary seismicity, rate of present-day creep and geodetic deformation, and geomorphic expression, the Calaveras fault is interpreted to consist of three primary sections. Our mapping focused on the northern and central segments, extending south from Danville, CA to San Felipe Lake, CA.

The primary focus of this research was to develop an up-to-date digital database of the northern and central Calaveras fault, using all readily available existing data. The digital dataset compiles information from previous fault investigations, Alquist-Priolo mapping and offset Quaternary deposits mapping with current state-of-knowledge research, helping to characterize this major fault.

Our results provide a comprehensive digital database with borehole, creep and paleoseismic data presented along with our interpreted fault strands. Fault strands are a synthesis of the available data, airphoto mapping and strand location interpretation presented at a 1:24,000 scale. Data and strands are provided as attributed shapefiles incorporated into the Northern California Quaternary Fault Map Database.

The Calaveras fault is considered a potential seismogenic source in probabilistic and deterministic seismic hazard analyses for existing and proposed infrastructure projects in the Bay region. Because of the importance of the Calaveras fault in the present-day seismotectonic setting of the San Francisco Bay region, having a up-to-date digital database of this major structural component is critical. Compilation of all three of the major fault sections forms one consistent, comprehensive database that can be accessed for scientific research, engineering-driven seismic hazard analyses, or public outreach.