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Source Characterization of 1944 Tonankai Earthquake from Observed and Simulated Damage Ratios Based on the Stochastic Representation of Complex Source Process and Damage Prediction Models for Old Wooden Houses

Session: Back to the Future: Innovative New Research with Legacy Seismic Data

Type: Oral

Date: 4/19/2021

Presentation Time: 05:30 PM Pacific

Description: 

It is very important to investigate the complex source process of repeated subduction-zone earthquakes for quantitative seismic hazard assessment. However, quantification of the rupture process for an earthquake before the implementation of strong-motion networks is difficult, if not impossible. In this study, we try to delineate the complex rupture process from the observed structural damage distribution in the past, instead of strong-motion records, based on the simulated strong motions and damage prediction models for old wooden-houses in Japan. We start to reproduce the observed damage ratios during the 1944 Tonankai earthquake, in which we have more than 50 cities and towns with reliable damage ratios higher than 1%. The strong ground motion waveforms are obtained from the statistical Green’s function and the heterogeneous source model. The site characteristic is obtained by our original method of converting the theoretical S-wave characteristic from the unified velocity model (by NIED) above the seismological bedrock in the Kanto and Tokai regions to the empirical site characteristics derived by the generalized spectral inversion. We first construct a heterogeneous source model with four asperities (SMGAs) as a standard model and prepare 36 heterogeneous source models in total, varying parameters of which are the location of hypocenters, the location of asperities, and their stress drops. Then, we calculate the strong ground motions from the prescribed complex source models and estimate the damage ratios of wooden houses using the corresponding damage prediction models as of 1944 to compare them with the observed damage ratios during the 1944 Tonankai earthquake. We found that the case with the second asperity stress drop of 60 MPa is the model that best explains the observed damage ratios. The proposed damage prediction scheme and the observed damage ratios provide us a prospect to clarify the detailed source rupture processes of the historical mega-thrust earthquakes in Japan.

Presenting Author: Eri Ito

Student Presenter: No

Authors