Abstract

On 26 December 2003, a destructive earthquake with an estimated Mw 6.5 occurred in southeastern Iran, causing extensive destruction in the city of Bam and its vicinity. The source of this shock was reported to have had a right-lateral strike-slip mechanism, and it initiated in a blind fault in the north–south direction. A regional network consisting of 23 strong motion stations (SSA-2 accelerographs) recorded the earthquake. The stations, located within 1–290 km of the epicenter, recorded peak ground accelerations between 0.01 and 0.99g. We employed the stochastic finite-fault method to simulate the recorded strong ground-motion data. The simulation is carried out using the Finite-Fault Simulation code (FINSIM) program (Beresnev and Atkinson, 1998a), which combines the stochastic ground-motion modeling technique with the kinematic model of rupture propagation. The fault is modeled as a rectangular plane with its area inferred from the distribution of the recorded aftershocks. The optimal size of the subfaults is selected as a function of the earthquake magnitude. Spectral analysis of the data indicates that the best match between the simulated and the observed spectra occurs for a radiation strength-factor of 1.6 and an average stress-parameter of 50 bars. The simulated peak amplitudes are in good agreement with the observed peaks. The observed and simulated spectra show a good agreement within the intermediate- and high-frequency ranges (≥1 Hz) at all stations. However, at low frequencies, the recorded amplitude spectra are generally larger at most stations. This can be viewed as the limitation of the homogeneous half-space medium included in the simulation model to generate surface waves, which are generally observed on real accelerograms. Similar to the recorded data, the simulated records at the stations north of the source show larger peaks with shorter durations as compared with those south of the source. The simulation technique used in this study reproduces the effect of source directivity: a large and relatively long-period pulse arriving shortly after the onset of the P-wave at the Bam station.

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