Abstract

We have examined the adequacy of the published KS3 and L1 slip distribution models developed for the MS = 7.4 16 September 1978 Tabas earthquake (Hartzell and Mendoza, 1991) by modeling the high-frequency accelerograms recorded at Dayhook, Boshrooyeh, and Tabas stations. The agreement in peak ground acceleration (PGA) and duration between data and simulated accelerograms was chosen as the criterion for the model adequacy. The fault was specified with a seismogenic rupture area 95 km long and 45 km wide. We used a semi-empirical simulation method in which accelerograms from an aftershock from the 1979 Imperial Valley earthquake were used to represent the radiation pattern of P, SV, or SH waves for a source-receiver geometry. The fault surface is divided into many subfaults. The contributions from these subfaults, weighted by the slip amounts, were lagged and summed to simulate the accelerograms of the main event. We computed accelerograms assuming constant rake and variable rake on the fault plane. The former was simulated using the SUM slip model (i.e., the slip model representing the vector sum of the slip components at every point on the fault), and the latter was simulated by summing the accelerograms generated by the slip models of the dip-slip and strike-slip faults. The influence of the rise time of the main event was investigated. The KS3 asperity model produces results marginally better than the L1 asperity model. The duration is predicted, consistent with the data. The peak amplitudes of the simulated ground motions remain within a factor of 1.5 and 3 of the recorded data at Dayhook and Boshrooyeh, respectively, for the variable-rake and within a factor for 2.5 at both stations for the fixed-rake angle (KS3 model). The large PGA recorded on the Tabas accelerograms could not be reproduced, which warrants additional study. A notable agreement was obtained in the response spectra at Dayhook. This study demonstrates that accelerograms generated by an earthquake in one tectonic region can be transported to another tectonic region so that they can be used to represent the empirical radiation pattern of the subfaults in simulating ground motions for a large event.

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