2020 Volume 20 Issue 7 Pages 7_120-7_132
It has been pointed out that earthquakes that occur in the Philippine Sea plate around Iyonada have inhomogeneous attenuation characteristics. One of the possible factors is the difference in attenuation between the continental plate and the Philippine Sea Plate and the heterogeneity of the horizontal attenuation structure. In this study, inhomogeneous attenuation structure, source and site amplification characteristics were separated from the observation records based on block inversion analysis that improves the method of Tomozawa et al. (2019) to estimate the inhomogeneous attenuation structure in the depth direction. As a result, the path region of the Philippine Sea plate was divided into the southwestern part of the Shikoku region and other regions, and became high-Q in the region where the upper surface depth of the Philippine Sea plate was deep. The short-period level of the 2001 Geiyo earthquake was estimated to be 3.12 × 1019 N m/s2. It is also shown that the bias of the spatial distribution of the residuals can be improved by taking into account the horizontal inhomogeneity of each plate.
