Phase-Dependent Site Effects Empirically Estimated

Abstract eng:
We developed a method for estimation of site effects in time function using observed records. So far, most of the empirical methods estimate the site effects with only amplitude spectra. Phase characteristics of the site effects have been assumed to be random in simulating strong ground motions. In this study, we attempt to separate the site effects in time domain from observed records. The site effects estimated in the above method are generally different for individual earthquakes. There are coherent site effects commonly included in different records and incoherent ones varying in different records. The coherent site effects are estimated by stacking the site effects in frequency domain synchronizing the onsets of S-waves from individual earthquakes. The incoherent site effects are estimated as power spectra subtracting the power spectra of the coherent site effects from those of the total site effects. The amplitude characteristics of the site effects are estimated as the sum of the amplitude spectra of the coherent ones and square root of the power spectra of the incoherent ones. The phase characteristics of the site effects are given the same as those of the coherent ones. The site effects in time domain are estimated by the inverse Fourier transform of those calculated above in frequency domain. We applied this method to estimating strong ground motions of the 2003 Tokachi-oki earthquake by the stochastic Green’s function method including the empirical site effects. We found the synthesized ground motions agreed well with the observed records.

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