An array of strong-motion accelerographs in Bear Valley, California

Abstract

Fifteen strong-motion accelerographs, each with the capability of writing the WWVB absolute time code on the recorded accelerogram, have been deployed in an elliptical array, at a station spacing of several kilometers, along the San Andreas Fault in the Bear Valley region of central California. Ten accelerograms were obtained for the June 22, 1973, earthquake (M = 3.9), located near the center of the array. Preliminary analyses of these accelerograms support previous suggestions that the crystalline rocks of the Gabilan Range possess higher material velocities and lower intrinsic absorption than do the Cretaceous and Cenozoic sedimentary rocks northeast of the fault zone. These accelerograms clearly indicate that a strong-motion accelerograph array of this sort can provide the basic data for source mechanism, wave propagation, and local ground-motion studies for earthquakes with magnitudes as small as 3.5-4.0.