ESTIMATION OF SOURCE, PATH AND SITE EFFECTS OF THE KYUSHU REGION

Study based on block inversion analysis using strong ground motion records

Abstract

　We estimated the source parameter, inhomogeneous attenuation structure and site effects of the Kyusyu region by using block inversion analysis [Tomozawa et al., 2019]. The obtained results are summarized as follows.

 

　1) Estimated inhomogeneous attenuation structure showed low-Q around the volcanic region. These results are consistent with previous studies which had evaluated the attenuation structure individually around the damaged earthquake.

　2) The short-period levels of large major earthquakes were estimated to be from about 1/2 to average of Dan et al.(2001). The source characteristics were estimated to be larger when the heterogeneity of Q values was taken into account.

　3) The site amplification factor was estimated to be smaller when inhomogeneous attenuation structure was taken into account for many stations. Considering that seismic waves were observed at stations where many records passed through highly attenuated zones around the volcano, the site amplification factor was estimated to be smaller than actual if a homogeneous attenuation structure was assumed for the entire region. We compared the theoretical amplification characteristics with those of bedrock sites, and found that the amplification factors were more consistent with the theoretical amplification factor when the inhomogeneous attenuation structure was considered.

　4) By considering the inhomogeneous attenuation structure, the value of variation was reduced to up to 15%, especially at high frequencies. The bias of the spatial distribution of residuals and standard deviation were also improved.