2018 Volume 18 Issue 1 Pages 1_77-1_88
Sakishima Islands, southwestern Japan, have high earthquake risk since they have often been damaged by strong ground motion and tsunami, and there are high risks of the disaster in the future in these islands. Although the S-wave structure of these islands, important for ground motion estimation, has been modeled as J-SHIS model by Japanese government (Headquarters of Earthquake Research Promotion), it has not yet been validated because of lack of data. We conducted array observation of microtremor survey at 13 sites on the islands. We modelled one-dimensional S-wave velocity structure for each site with the inversion of estimated phase velocity. All the S-wave structures are successfully modeled with four velocity layers. Depth of the seismic bedrock, velocity layer over 3 km/s, differs with islands; it is 1.6 to 2.0 km at Miyako islands, whereas it is 0.2 to 0.5 km at Yaeyama islands. Based on these results, we showed the averaged Vs values of each layer and the depths of layer boundary at each site for construction of subsurface 3D model.
