DETERMINATION OF THE SUBSURFACE STRUCTURE OF HAMADA CITY, SHIMANE PREFECTURE USING MICROTREMOR EXPLORATION

Abstract

Serious damages occurred by 1872 Hamada Earthquake in Hamada City, Shimane Prefecture. It is supposed that the damage influenced the subsurface structure. Therefore, microtremor observations were carried out to determine the subsurface structures of the Hamada City, Shimane prefecture. The subsurface structures were determined by S-wave velocity structure models obtained at the array observation 4 sites and predominant period distribution at 3-components observation 44 sites. The Swave velocities of alluvial layers were 100-150m/s. The predominant period was 0.2-0.8 period that H/V were clear single peak models in areas along the Hamada River. It was found that soft alluvial layers were distributed whole area from S-wave velocity structure. Depth to bedrock (S-wave velocity is 800m/s layer) was about 50m maximum and the depth to a bottom layer (S-wave velocity is 3000m/s layer) was about 800m maximum.