[S-CG60] Shallow Fault Zone Structure and Seismic Hazard Assessment

[SCG60-P01] Investigation on estimation of seismic source fault length including shallow long period ground motion generation area

*Naoto Inoue¹ (1.Geo-Research Institute)

Keywords:fault displacement of surface rupture, long period ground motion generation area, Fault length

Strong ground motion prediction based on the characterized source model is widely used in Japan for seismic evaluations of important facilities. The procedure of constructing the characterized source model is provided as the ‘recipe’. In recent years, with the increasing number of seismic records near surface ruptures, it is necessary to consider a long-period motion generation area (LMGA) in the shallow layer to reproduce displacement records. The construction method of the characterized seismic source model with LMGA is currently under discussion in the ‘recipe’, and the establishment of the setting method is an important issue in considering the fault displacement hazard. In this study, the estimation of shallow subsurface slip area from the displacement distribution of surface ruptures has been attempted. However, the displacement distributions of surface ruptures are complicated, and it is difficult to identify a large displacement area as a simple rectangular shape. To model for probabilistic fault displacement hazards, many previous studies have presented models approximating surface earthquake fault displacement distributions with functions such as quadratic, elliptical, and bi-linear functions. In many models, the displacement is large near the central part of the fault. Focusing on the average displacement among the parameters obtained from the surface seismic fault displacement, a method of setting the LMGA region where the displacement is greater than the average displacement was investigated. Organizing the surface earthquake fault displacement distribution of past earthquakes and the source inversion model, the length of the region where the average displacement amount or more (here it is assumed to be the LMGA length) and the source fault length were extracted. The relationship between these extracted lengths and surface earthquake fault length was obtained. Based on the estimated regression equations, the setting as a prediction problem is summarized as shown in the figure. In the poster, setting examples of actual prediction problems are presented.

This study was conducted as part of the contract research in FY2019, FY2020 and FY2021, sponsored by the Secretariat of Nuclear Regulation Authority, Japan.