Source Modeling of Subduction-Zone Earthquakes and Long-Period Ground Motion Validation in the Tokyo Metropolitan Area

Abstract eng:
The national seismic hazard map of Japan indicates 30-year probability in the Tokyo metropolitan area to be controlled by megathrust earthquakes along the Nankai trough of the Philippine sea plate. This indicates that source modeling and realistic ground-motion prediction for distant subduction-zone earthquakes are quite important for disaster mitigation and hazard assessment in the Tokyo metropolitan area. We have performed long-period ground motion validation for the hypothetical Tokai (> 2 s) and Tonankai (> 4 s) earthquakes using characterized source models and integrated 3D velocity structure model. The characterized source model consists of asperities and background area. The size and slip of the asperities are constrained by the source scaling of asperities for subduction-zone earthquakes, where the scaling is based on the compilation of past slip inversion results. We adopted the 3D velocity structure models of basin, ocean, and plate constructed by integrating refraction, reflection, borehole, microtremor, and gravity data as well as ground motion spectra. The distribution of simulated long-period ground motions by the 3D finite difference method well reflects the velocity structures in the Kanto basin, and the oceanic structure with the sedimentary wedge which contributes to further propagation of the long-period ground motions. We have confirmed that long-period ground motions at a period of 7-10 s are significantly developed in the Kanto basin, indicating that the impact of damaging long-period ground motion from the future megathrust events against the Tokyo metropolitan area.

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