Abstract
We have developed a method to simulate strong ground motions by combining the stochastic Green's function (SGF) and 3-D attenuation structure. The calculation procedures of our method are as follows. (1)To give source spectra for sub-fault events. (2)To calculate basement spectra considering 3-D Qs structure. (3)To calculate ground surface spectra by multiplication of the site factors to basement spectra. (4)To make time history of ground motions using ground surface spectra and envelope function (Boore, 1983). (5)To create main shock ground motion by superimposing the ground motions from sub-fault events considering lapse time: fault rupture and travel time. (Irikura, 1986) In this study, we reproduced strong motions of the 2003 Tokachi-Oki earthquake(M8) and the 2011 Off the Pacific Coast of Tohoku, Japan earthquake (M9) by using this method. Target sites to evaluate are ground surfaces of the K-NET and the KiK-net observation stations. The 3-D Qs model and site amplification factors estimated by Nakamura (2009) were used in this study. To show validity of this method, we compared calculation results by using the 3-D Qs model with by a uniform Qs model; Qs=100f1.0. The response spectra of ground motion calculated from the uniform Qs model are underestimated in the long distance areas, e.g. Kinki and Hokkaido in case of the 2011 earthquake, whereas the response spectra using the 3-D Qs model were well reproduced the observed ones. Seismic wave propagates in deeper part for longer distance travels without attenuating. It is necessary to consider the 3-D Qs structure in evaluating the ground motion distribution in a broad area.
