SEGJ Technical Conference

Structural Survey and Seismic Observation Performed in Hokusetsu Area (Part 1) Subsurface structures estimated by microtremor array observation

Abstract The northern area of the Osaka prefecture between the Hokusetsu mountains and the Osaka basin is complicated in the geological structure. To investigate the geological structure in this area, microtremor array observations are conducted at two sites (graben and hill site). We deployed seven sensors in triangular arrays with the maximum radius of about 30m, 100m and 500m. Using the Expanded SPAC method, we obtained phase velocities of about 0.3-2.0km/s for the frequency range from 0.5 to 10Hz. From the obtained phase velocities for Rayleigh waves and the result of reflection survey, we estimate the underground structure models. The basement (Vs>3km/s) depth of the estimated structure model in t in the graben is about 1.3km, and in the hill zone is about 0.6km.