A three-dimensional dislocation model for the San Fernando, California, earthquake of February 9, 1971

Abstract

The data from five strong-motion accelerograph stations centered above and surrounding the fault are used to develop an approximate three-dimensional dislocation model for the San Fernando earthquake. In the resulting model, the dislocation originates near the instrumentally determined epicenter at a depth of 9.2 km and then propagates southward and upward with a velocity of 2 km/sec. Calculated dislocation amplitudes of about 10 m in the hypocentral region have been found to decay to about 1 m toward the center of the fault and then build up again to about 6 m just before the fault intersects the ground surface in the San Fernando Valley. The assumed fault area of 130 km^2 and the assumed rigidity µ = 3 × 10^(11) dyne/cm^2 give a moment M_0 = 1.53 × 10^(26) dyne-cm. This study indicates that, with several strong-motion accelerographs suitably located in the epicentral region, it is possible to find a kinematic faulting process associated with the periods of ground motion which are longer than about 1 sec.