TRIGGERED SLIP ON THE CALAVERAS FAULT DURING THE MAGNITUDE 7.1 LOMA-PRIETA, CALIFORNIA, EARTHQUAKE

After the magnitude (M) 7.1 Loma Prieta earthquake on the San Andreas fault we inspected selected sites along the Calaveras fault for evidence of recent surface displacement. In two areas along the Calaveras fault we documented recent right‐lateral offsets of cultural features by at least 5 mm within zones of recognized historical creep. The areas are in the city of Hollister and at Highway 152 near San Felipe Lake, located approximately 25 km southeast and 18 km northeast, respectively, of the nearest part of the San Andreas rupture zone. On the basis of geologic evidence the times of the displacement events are constrained to within days or hours of the Loma Prieta mainshock. We conclude that this earthquake on the San Andreas fault triggered surface rupture along at least a 17‐km‐long segment of the Calaveras fault. These geologic observations extend evidence of triggered slip from instrument stations within this zone of Calaveras fault rupture. © 1990 by the Chinese Geophysical Society