SEGJ Technical Conference

Local site effects in the western edge of Ashigara Valley, estimated by the microtremor survey

Abstract Broadband earthquake ground motions were observed in the entire Japan, during the 2011 off the Pacific coast of Tohoku earthquake. In the Ashigara Valley, which is located in the south-west of Kanto Basin, the earthquake ground motions for periods of several seconds were dominated. Especially, the ground motions for a period of 2 to 3 seconds were extremely large in the western edge of Ashigara Valley. In this study, we estimated shallow S-wave velocity structures by array microtremor observations for the small area of 2km x 2km, in which the large displacement response for the base-isolated houses was observed during the main shock. The site amplification factors obtained using the estimated shallow S-wave velocity structures has clearly locality in this area. In the site which large displacement responses for the base-isolated houses were observed, the site amplification factor for a period of 2 seconds were significantly dominated.