[S-CG49] 島弧の構造・進化・変形とプレート沈み込み作用

[SCG49-P06] Constructing a 3D seismic S-wave velocity model of the Nankai Trough

*Ayako Nakanishi¹、Yanfang Qin¹、Gou Fujie¹、Katsuhiko Shiomi²、Shuichi Kodaira¹、Narumi Takahashi^1,2、Takeshi Nakamura³ (1.Japan Agency for Marine-Earth Science and Technology、2.National Research Institute for Earth Science and Disaster Resilience、3.Central Research Institute of Electric Power Industry)

キーワード：Nankai Trough, 3D model, S-wave

To predict strong ground motion and tsunami and seismic hazards as well as determination of hypocenters with high-resolution, three-dimensional (3D) seismic velocity model must first be determined. Particularly in the Nankai Trough, it is an urgent issue for disaster prevention. Nakanishi et al. (2018) first proposed 3D seismic P-wave velocity (Vp) model around the Nankai Trough mainly based on results of offshore wide-angle seismic refraction surveys. Seismic S-wave and density information of the shallow sediments will improve not only the accuracy of hypocenter determination but also the reliability of earthquake cycle simulation and strong motion prediction. However only a few results related to seismic S-wave velocity (Vs) structure based on offshore wide-angle seismic surveys were proposed so far (e.g., Takahashi et al., 2002), because the direct S-wave cannot be generated by controlled source in the seawater. Recently, based on both onshore and offshore seismic observation data, 3D seismic velocity structure including Vs information around the Nankai Trough is obtained by Yamamoto et al. (2017). Moreover, one-dimensional Vs structures beneath DONET stations are estimated by using displacement-pressure ratios of the Rayleigh wave (Tonegawa et al., 2017). In this presentation, we suggest our strategy for constructing a 3D seismic S-wave model by using those existing results combined with the experimental conversion formula from Vp to Vs (e.g., Brocher, 2005) and show our progress including the upgrade of Vp model and geometry of the subducting plate at present. This study is part of ' Research Project for Disaster Prevention on the great Earthquakes along the Nankai Trough' funded by Ministry of Education, Culture, Sports, Science and Technology, Japan. This work is partly supported by JSPS KAKENHI Grant Number 19H01982.