A hybrid method for simulating near-source, broadband seismograms: Application to the 2003 Bam earthquake (Mw 6.5)

The main objective of this article is to simulate the three components of near-source ground shaking recorded at Bam station, close to the causative fault, during the destructive the 2003 Bam earthquake, where were strongly influenced by rupture directivity effect. A hybrid technique composed of the theoretical Green's function, finite element and finite difference method proposed by Spudich et al. (1987, 2003) (COMPSYN) and a ω2-based finite-fault approach proposed by Beresnev and Atkinson (1998a) (FINSIM) are used for generating seismograms at low and high frequencies respectively. A Genetic algorithm technique is developed for minimizing the differences between the recorded and simulated data incorporating parameters within a predefined upper/lower bound's values previously estimated for main shock by other investigators. Two different faulting models, consist of a straight line segment and a straight line segment followed by a slightly north-eastward branch, are used.The simulated three component seismograms at Bam station, in terms of elastic response spectra, are validated by comparing the simulated time series with those of the observed data. Moreover, the pulses involved in the recorded time series due to the rupture directivity are estimated and compared with those of the observed data. A sensitivity analysis is performed for recognizing the influence of model parameter changes, such as focal mechanism (strike, dip and rake), rise-time, rupture velocity and hypocenter location on the simulated seismograms. Relatively good match of the simulated and observed time series, particularly the two faulting models, confirm the potentiality of the proposed technique and the suitability of seismological model parameters used. This technique can be used for specific site hazard analysis of the Bam region and linear/nonlinear dynamic analysis of structures where were damaged during the Bam earthquake particularly for retrofitting the well known international adobe buildings of Arg-e-Bam.