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Strong-Motion Simulation of the 1944 Tonankai Earthquake Along the Philippine Sea Plate Based on the Damage Ratios of Wooden Houses With In-Situ Measurements of Microtremors at the Population Centers of Heavily-Damaged Villages and Towns

Description: 

For precise prediction of the future megathrust earthquakes along the Philippine Sea Plate in western Japan, we need both representation of the complex source process and Green’s function from the fault to the sites. The latter can be obtained through a statistical analysis of many observed records, as Nakano et al. (BSSA, 2015) did by using the generalized inversion technique, while the former needs delineation of the source processes for earthquakes that occurred in the past. It is necessary to construct source processes for not only earthquakes with strong-motion data but also those without because they occurred before the deployment of strong-motion networks. For those old earthquakes, we need to use observed structural damage ratios (SDR) as a substitute for strong-motion seismometers in the heavily-damaged areas. As the first step of investigations, we performed a parametric study for the 1944 Tonankai earthquake (M8.0) to find the best scenario (Ito et al., SSA meeting, 2021).

We found that we could reproduce observed SDRs up to 40%, however, we underestimated SDRs at several villages and towns with higher SDRs. In the first stage, we used horizontal site amplification factors (HSAFs) at these sites based on the theoretical 1D transfer function with empirical correction. To fill the gap, we measured single-station microtremors at the population centers of the heavily-damaged villages and towns in March 2022. From microtremor H/V ratios we converted them into pseudo earthquake H/V ratios and then we applied the VACF method (Ito et al, BSSA 2020) to convert them into HSAFs. With these observed HSAFs, we tried to reproduce the SDRs for the same best source model. As a result, the SDRs by new HSAFs slightly increased, however, there remain differences at higher SDR sites. This means that we need to explore further the possibility of improvement for the empirical correction scheme on the soil nonlinearity at these sites, which reduced amplitude significantly.

Session: Future Directions in Physics-based Ground-motion Modeling in Preparation for the Fall 2023 Meeting [Poster]

Type: Poster

Date: 4/18/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Eri Ito

Student Presenter: No

Invited Presentation: 

Authors