Validation of the Osaka basin velocity model by waveform simulation using sources inverted with reciprocal Green’s functions

Abstract

To advance the methodology for validating velocity models by waveform comparison, we estimated source parameters for small magnitude earthquakes that can be approximated by point sources. Instead of using published source models, we used the reciprocity method to calculate 3D Green’s functions using the target velocity structure itself, and then inverted the earthquake sources. This method greatly reduces the calculations required compared to a full inversion of the source mechanism, depth, and source duration (risetime), making it possible to reproduce input ground motions in the target basin. Here, we validated the Japan Integrated Velocity Structure model of the Osaka basin using five earthquakes around the Osaka basin; these earthquakes allowed us to investigate the impact of the incident waves’ propagation directions. We first estimated source parameters using records at control bedrock sites surrounding the Osaka basin to reproduce the input ground motions. Then, we conducted a 3D finite-difference simulation for sites within the basin. By mapping the distributions of misfit values for individual waveforms, peak ground velocities, and response spectra, we were able to identify areas in the basin that require additional tuning of the velocity model.Graphical