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Strong Shaking Predicted in Tokyo From an Expected M7+ Itoigawa-Shizuoka Earthquake

Marine A. Denolle, Pierre Boué, Naoshi Hirata, & Gregory C. Beroza

Published May 12, 2018, SCEC Contribution #7914

The Itoigawa-Shizuoka Tectonic Line (ISTL) is a major oblique left-lateral crustal fault that is expected to host M7+ events in the near future. Its proximity to the Kanto sedimentary basin poses a threat to the population of Metropolitan Tokyo. This study constructs scenario earthquakes on the ISTL by predicting ground motions using virtual earthquakes. We use the ambient seismic field to calculate the cross-correlation function that we assumed proportional to the elastodynamic Green tensor between Hi-net stations, located above the ISTL, that act as virtual sources and MeSO-net stations, located in the Kanto Basin, that act as receivers. The virtual earthquake approach \citep{Denolle13,Denolle14a} allows us to predict ground motion from a suite of 270 kinematic sources. We find that the ground motions are high enough that non-linear effects, which we do not model, will likely reduce the amplitudes. We also find that the shape of the sedimentary basin greatly alters the shaking by amplifying long period ground motions as seismic waves refract on the basin edge. This is particularly true for the vertical ground motions. Additionally, we quantify ground motion variability due to source uncertainty, surmise that ground motions are log-normally distributed with regard to source uncertainties, and suggest that the variability is affected (locally either enhanced or reduced) by the basin shape. Finally, we find a coupling point between source and wave paths for epicentral locations on the ISTL that generate as much as twice the shaking as the equivalent unilateral ruptures, despite directivity orientation that would favor southward ruptures.

Denolle, M. A., Boué, P., Hirata, N., & Beroza, G. C. (2018). Strong Shaking Predicted in Tokyo From an Expected M7+ Itoigawa-Shizuoka Earthquake. Journal of Geophysical Research: Solid Earth, 123(5), 3968-3992. doi: 10.1029/2017JB015184.