A FAULT MODEL WITH VARIABLE SLIP DURATION FOR THE 1989 LOMA-PRIETA, CALIFORNIA, EARTHQUAKE DETERMINED FROM STRONG-GROUND-MOTION DATA

A finite-fault model with variable slip duration is inferred from stro ng-ground-motion data for the Loma Prieta earthquake. Unlike previous models, slip duration is found to be consistent with fault width scali ng. Slip duration varies between 1 and 6 sec at points along the fault surface with values between 3 and 6 sec, where slip amplitudes obtain or exceed the average slip of 98 cm. Modest high-frequency modificati ons of the slip function shape greatly enhance the data fit without si gnificantly changing the inferred static offset or rupture characteris tics. This model exhibits bilateral rupture with the propagation rate of the main energy release of 3 km/sec or less. The moment is 2.3 X 10 (26) dyne-cm, and the largest slip amplitudes occur northwest of the h ypocenter. The rake varies with position along the fault from dominant ly strike slip in the southeast to dominantly reverse slip in the nort hwest.