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A Velocity Structure Model for Ground Motion Simulation in Japan

Description: 

Japan is in a complex tectonic setting with various subducting plates, and most urban areas are located on sedimentary basins. These lead to 3D complicated velocity structures, which have significant impacts on seismic ground motion in Japan. Therefore, for accurately simulating seismic ground motion, it is essential to accurately model the 3D velocity structure throughout Japan. Koketsu et al. (2009) proposed a standard procedure for modeling a regional 3D velocity structure in Japan, simultaneously and sequentially using various datasets such as those of refraction/reflection experiments, gravity surveys, surface geology, borehole logging, microtremor surveys, and earthquake observations. We applied this procedure to northeastern and central Japan in 2009, and to southwestern (SW) Japan in 2011. We then constructed version 1 (V1) of the Japan Integrated Velocity Structure Model by combining these regional models in 2012. A revised version of this (V1R) was published in 2023.

We have made the following modifications to V1R to create version 2 (V2): (1) the seismic basement in SW Japan was corrected to be less complex; (2) the structure of the accretionary prism along the Nankai Trough was revised to fit the relationships of Baba (2005a); (3) narrow accretionary prisms were added along the Japan Trench and Sagami Trough based on Baba (2005b). We have first performed a ground motion simulation for the 2004 earthquake off the Kii Peninsula using V2. Watanabe et al. (2014) also conducted a simulation for the earthquake using V1. In their results, the duration of ground motion in the Tokyo lowland was reproduced, but there is a problem with the amplitude. Our simulation with V2 improves the problem considerably, and slight overestimation is solved by introducing sea water into the simulation. We have secondly performed a ground motion simulation for the 2011 Tohoku earthquake using V2. The results of the simulation by Kawabe et al. (2013) using V1 show slight underestimations in the Tohoku to Kanto region, and slight overestimations in the Kinki region. These problems are generally improved in our simulation.

Session: Numerical Modeling in Seismology: Theory, Algorithms and Applications - II

Type: Oral

Date: 4/17/2025

Presentation Time: 11:15 AM (local time)

Presenting Author: Kazuki

Student Presenter: No

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