A Three-dimensional Dislocation Model for the San Fernando, California, Earthquake

The data from five strong-motion accelerograph stations centered above and surrounding the fault are used to develop an approximate three-dimensiunal 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 kin/see. Calculated dislocation amplitudes of about 10 m in the hypucentral 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 p = 3 × 1011 dyne/cm 2 give a moment M o = 1.53 × 1026 dyne-cm. This study indicates that, with several strong-motion accelerographs suitably located in the epicentrai region, it is possible to find a kinematic faulting process associated with the periods of ground motion which are longer than about I sec.