SEGJ Technical Conference

Peak distribution of Micro-tremor H/V spectra in Kochi Plain and it's relation to distribution of estimated seismic intensities and hazards due to previous Nankai Earthquakes

Abstract Toward a better understanding of site amplification effect in Kochi Plain, we conducted micro-tremor H/V spectral analysis in Kochi Plain at more than 1100 points. We determine dominant periods and secondary peak periods which appear shorter period than dominant peak. Based on comparison with geological model using boring cores, dominant periods correlate with depths of the basements, while secondary peak periods correlate with thicknesses of the Holocene layer. Longer dominant periods (>0.9s) appear in Urado Bay region, where estimated seismic intensities are more than 6 for Showa, and Ansei Nankai earthquakes. In this region, thicknesses and Vs of Holocene layer are 30m and 160m/s, respectively, while Vs values of Holocene layer for other region is 220 m/s. Smaller surface Vs and longer dominant period causes severe damage in this region. Locations of taken pictures of hazards by Showa Nankai Earthquake coincide with above interpretation.