A Study on the distribution of shear wave polarization anisotropy in the Miyazaki Plain and its neighboring areas, Kyushu Island, Japan

Ogawa, Hiroki; Hiratsuka, Shinya*; Asamori, Koichi; Shimada, Koji   

One of the issues related to the assessment of geosphere stability for long-term isolation of HLW is the crucial effect of geofluids such as slab-related fluid on the disposal site. As the fore-arc region of Kyushu Island, Japan, is related to subduction of the Philippine Sea Plate, it is believed that the Miyazaki Plain and its neighboring areas have been influenced by slab-related fluid. With a view to capturing pathways of slab-related deep-seated fluid by means of subsurface seismic anisotropy, we performed a shear wave splitting analysis by utilizing seismic waveform data recorded at stations located throughout Miyazaki prefecture. It reveals that many of the stations show the orientation of the seismic anisotropy parallel to the axes of the maximum horizontal compressional stress, while several stations in the Miyazaki Plain show the orthogonal orientation to that of these stations. Regarding the strength of the seismic anisotropy, relatively large values are partially distributed in the southern part of the Miyazaki Plain and the area above the low S-wave velocity anomaly estimated in the previous study.