Non-Stationary Analysis of Bam 2003 Earthquake Record

Abstract eng:
Strong ground motion is widely investigated by methods designed for stationary processes, as are power and Fourier or response spectra. In fact, it is a highly non-stationary phenomenon, whose characteristics are strongly linked to a theoretically well understood, but practically poorly apprehensible physical background. The catastrophic 2003 Bam, Iran, Earthquake has been analysed by others from seismological and engineering aspects, but frequency related parameters as well as non-stationary characteristics of this event have not been investigated so far. In this paper, we will investigate non-stationary properties of local strong motion by means of Evolutionary Power Spectra as well as by Time-dependent Principal Correlation Axes (TPCA) – a family of methods for local strong motion analysis developed by Bretschneider & Scherer (2000a 2000b, 2004, 2006), similar to well-known Principal Component Analysis. We use these methods to identify major wave phases and estimate the directions of motion as well as other specific characteristics of the corresponding wave trains. The findings for the strong motion record at Bam are then discussed with respect to source dynamics. Our findings on the faulting process are in very good agreement to those from aftershock analysis by Nakamura et al. (2005).

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