Simulation of broadband strong motion based on the empirical green’s spatial derivative method

Abstract

In our previous studies (Ohori and Hisada, Zisin 2(59):133–146, 2006, Bull Seismol Soc Am 101:2872–2886, 2011), we simulated the strong-motion records of the mainshock (MJ5.4) of the 2001 Hyogo-ken Hokubu earthquake, Japan, on the basis of the empirical Green’s tensor spatial derivative (EGTD) estimated from data of 11 aftershocks (MJ3.5–4.7). The agreement between the observed and calculated waveforms at the closest station in source distance was satisfactory over a long duration, and the amplitude was well reproduced. But considering the lowest corner frequency of about 1.0 Hz for the mainshock, we targeted 0.2–1.0 Hz band-pass-filtered velocity waveforms. In the present study, we tried to simulate the broadband strong motions beyond the corner frequencies for the same events as in our previous studies mentioned above. To correct the discrepancies among the corner frequencies of events, we assumed the scaling law based on the ω−2 model (Aki, J Geophys Res 72:1217–1231, 1967) and compensated the spectral amplitude decay beyond the corner frequency. After estimating the EGTD from 11 aftershock events using 0.2–10 Hz band-pass-filtered waveforms, we simulated the strong-motion records for the mainshock and aftershocks. In simulation of each event, the EGTD elements were multiplied by the moment tensor elements followed by summation and corrected in the spectral amplitude, taking the corner frequency of each event into account. As example results, the simulated waveforms at the closest epicentral distance was compared with the observed ones. The agreement between the calculated and observed waveforms was acceptable for most of events.