Identification of the velocity structure model of Kyoto basin for strong motion prediction using observed earthquake and microtremor motions

Abstract

We need to evaluate the underground structure properly and validate previously proposed ground structure models with the observed earthquake and microtremor motions to prevent future catastrophic disasters in urban areas. In this study, we focus to Kyoto City which lies on the Kyoto basin. We first used earthquake data observed at Fire Stations in Kyoto City and calculated the Horizontal-to-Vertical Spectral Ratios (HVRs). Based on the diffuse field theory and the Hybrid Heuristic Search Method, we identified the velocity structure at each of the earthquake observation stations. Then, from the point of view that a unified velocity structure should be used in the final three-dimensional basin model, we derived a unified velocity structure for each earthquake observation station. From the unified velocity structure we calculated the theoretical microtremor HVR based on the diffuse field theory and changed the thickness of the layers to fit the peak frequency with the microtremor HVRs observed in Kyoto City to modify the velocity structure at the microtremor observation sites. Finally, we compared the identified velocity model with the previously proposed Kyoto basin model and it showed good correspondence. Also, the simulated velocity waveform showed a very good fit with the data, so we conclude that the identification method we proposed in this study is valid for strong motion predictions of future earthquakes.