Stochastic strong-motion simulation of the Umbria-Marche earthquake of September 1997 (Mw 6): comparison of different approaches

Abstract

Abstract We simulated strong-motion records from the Umbria–Marche, central Italy, earthquake (Mw 6) of September 1997 using a frequency-dependent S-wave radiation function. We compared the observed acceleration spectra, from strongmotion instruments located in the near field and at regional distances, with those simulated using the stochastic modeling technique of Beresnev and Atkinson (1997, 1998), and modified to account for a frequency-dependent radiation pattern correction. By using the frequency-dependent radiation function previously obtained by Castro et al. (2006), we reduced the overall fitting error of the acceleration spectra by about 9%. In general, we observed that the frequency-dependent radiation pattern correction has a small effect on the spectral amplitudes compared with site effects, which is an important factor controlling the strong-motion records generated by the 1997 Umbria–Marche earthquake. In addition, we modeled the observed ground-motion records using the dynamic corner frequency model of Motazedian and Atkinson (2005) to reproduce the directivity effects, reducing the average error of the spectral amplitudes by 24%. We concluded that although the frequencydependent radiation pattern correction affects the frequency content of the spectral amplitudes simulated, site and directivity effects are more relevant.