FAULTING MODEL FOR THE 1979 IMPERIAL VALLEY EARTHQUAKE.

Abstract

By comparing synthetic particle velocities with the near-source strong motion data, a faulting model for the 1979 Imperial Valley earthquake was constructed. The calculation of the synthetic seismograms takes into account the vertical inhomogeneity of the elastic parameters in the Imperial Valley and the spatial variation of the slip rate parameters on the fault plane. The faulting model has the following principal features: Faulting occurred on the Imperial fault and on the Brawley fault, rupture on the Brawley fault being triggered by rupture on the Imperial fault; The Imperial Fault is a plane 35 km long and 13 km wide with a strike of 323 degree , measured clockwise from north, and a dip of 80 degree NE; Faulting on the Imperial fault is primarily right-lateral strike slip with a small component of normal dip slip in the sediments at its northern end; The rupture velocity on the Imperial fault is highly variable; Although the slip on the Brawley fault contributes only about 4% of the total moment, it greatly affects the ground motion at nearby stations; and The total seismic moment is 6. 7 multiplied by 10**1**8 N m where the Imperial fault contributes 6. 4 multiplied by 10**1** 8 N m and the Brawley fault contributes 2. 7 multiplied by 10**1**7 N m.