Modeling the Shallow Subsurface Structure in the Urban Area of Kochi City

Abstract

In this paper, we constructed a shallow underground structure model of Kochi city for the area of 10.5 km in east-west by 5.5 km in south-north direction with a resolution of 125 m. By compiling the geological information opened by the Committee of Kochi Geo-Hazard Evaluation (2011), we constructed a multi-layered model embedded over the engineering bedrock with the S-wave velocity of 700 m/s. Based on our newly developed model, dispersion characteristics of theoretical surface waves at two sites were calculated and agreed well with observed ones derived from our microtremor-array experiments. The predominant periods along two north-south lines calculated from our model were coincident with the previous observational data shown by Mori at al. (2001).We also conducted a seismic response analysis using the synthesized ground motion from the Central Disaster Management Council of Japan (2003) as the input motion of basement of the developed subsurface structural model. We found that the area where relatively high seismic intensity was predicted was well corresponding to the severely damaged area during the 1946 Nankai Earthquake.