A RUPTURE MODEL FOR THE 28 JUNE 1992 LANDERS, CALIFORNIA, EARTHQUAKE

We have modeled displacement time histories to infer the large-scale rupture process of the 28 June 1992 M 7.4 Landers, California, earthquake. We have used integrated accelerograms from four TERRAscope stations at distances between 70 and 150 km The earthquake process consists of unilateral rupture propagation, 3 km/s, on two distinct segments with different strikes: N10-degrees-W and N40-degrees-W. The two segments are 20 and 30 km long with constant slip of 3.5 m and 5.2 m, respectively. The excitation of surface waves, resulting from a low-velocity surficial layer, plays a critical role in matching the synthetic waveforms to the observed displacements. The displacements, due to both body waves and surface waves, are strongly affected by directivity. Matching the synthetics to the data requires a one second delay between the end of rupture on the first segment and the initiation of rupture on the second segment. The seismic moment of the subevents are 2.8 x 10(19) N-m and 8.4 x 10(19) N-m, leading to a total moment of 1.12 x 10(20) N-m (M=7.4).