SYMPATHETIC FAULT MOVEMENT ON THE SULFUR SPRINGS THRUST FROM THE 1906 SAN FRANCISCO EARTHQUAKE, SOLANO COUNTY, CALIFORNIA

A rarely discussed paragraph in the Carnegie Report on the 1906 San Francisco earthquake (Lawson, 1915, v. 2, p. 213) describes deformation in the Saint John's quicksilver mine in Solano County, California. The deformation occurred at the same time as the San Francisco earthquake. The earthquake occurred during a shift change, and when the morning shift entered the mine, the miners observed zones where tunnels and supports had shifted several feet. The mine is located in the Sulfur Springs thrust zone that is 25 to 30 miles east of the San Andreas Fault in central Solano County. Our analysis suggests that the mine deformation represents sympathetic movement on the Sulfur Springs thrust from the 1906 earthquake on the San Andreas Fault. There is no indication that the deformation was caused by landsliding or localized failure within the mine. The mine is located just south of a westward bend in the Sulfur Springs thrust. The mine deformation pattern is consistent with northward movement of large blocks within the Sulfur Springs thrust zone.