EVALUATION OF SHALLOW S-WAVE VELOCITY STRUCTURES IN THE KOIWAGAWA AREA MOST AFFECTED BY THE 2019 OFF THE YAMAGATA PREFECTURE EARTHQUAKE

Abstract

 A maximum instrumental seismic intensity of 6+ was observed in near source area during the 2019 off the Yamagata Prefecture earthquake, Mj 6.7. The Koiwagawa area of Yamagata Prefecture located in near source area, was one of the areas most affected by this earthquake. In the Koiwagawa area, about one third of the wooden houses suffered damage to their roofs. In this study, we investigated the surface layer S-wave velocity structures of this area by surface wave survey. The results show that shallow subsurface layers with low shear wave velocity are distributed in a thickness of 3 m to 10 m. The thicker these layers are, the higher the damage rate of the roof tiles.