[H-DS06] Tsunami and tsunami forecast

[HDS06-P07] Comparison of tsunami hazard curves and historical tsunami exceedance frequencies in western Kii Peninsula, Japan

*Naoki Tanaka¹, Toshitaka Baba² (1.Department of Civil and Engineering,Division of Science and Technology, Graduate School, and Technology for Innovation,Tokushima University, 2.Graduate School of Industrial Science and Technology, Tokushima University)

Keywords:Tsunami Hazard Curve, Tsukuba Trace High, Nankai Trough earthquake, Kii Peninsula

This study constructed tsunami hazard curves in the western Kii Peninsula for the Nankai Trough earthquakes and compared them with the historical tsunami exceedance frequency. We used the 3480-case Nankai Trough earthquake models proposed by Fujiwara et al. (2020) for the tsunami source scenarios. In tsunami calculations, we solved the nonlinear long wave equations by the finite difference method with a three-layer nesting grid system to reduce the tsunami calculation load. The minimum grid spacing was set to 2 arc-sec. We relied on the G-R law from the JMA earthquake catalog to determine earthquake occurrence probabilities. We used limited data in the JMA catalog, earthquakes from 1919 to 2020 in the Nankai subduction zone with depths shallower than 50 km, greater than M5.0, and reverse fault earthquakes. We used the tsunami trace database of the International Research Institute of Disaster Science, Tohoku University, to estimate the historical tsunami exceedance frequency. We included the Nankai Trough earthquakes since 1498. For missing data in tsunami trace height, we calculated them by using proposed fault models of past earthquakes (Annaka et al., 2003). We counted events exceeding a designated tsunami height (H) at a given point. We divided the number of events by a period length (570 years) to obtain the historical tsunami exceedance frequency. The estimated historical tsunami frequency almost agrees with tsunami hazard curves. However, it deviated from the 95% confidence limits of the tsunami hazard curves in the town of Imani in the southwestern part of Wakayama Prefecture. The deviation may be because of a V-shaped bay and artificial changes on the coastline in the bay. We will reconstruct the past topography and re-investigate the tsunami hazard curves.