Nationwide tsunami hazard assessment project in Japan

Monday, 15 December 2014: 10:50 AM
Kenji Hirata1, Hiroyuki Fujiwara2, Hiromitsu Nakamura3, Masaki Osada1, Tatsuo Ohsumi1, Nobuyuki Morikawa1, Shin'ichi Kawai1, Shin Aoi1, Naotaka Yamamoto1, Hisanori Matsuyama4, Nobuhiko Toyama5, Tadashi Kito5, Yoichi Murashima6, Yasuhiro Murata6, Takuya Inoue6, Ryu Saito6, Shinichi Akiyama7, Mariko Korenaga7, Yuta Abe7 and Norihiko Hashimoto7, (1)NIED National Research Institute for Earth Science and Disaster Prevention, Tsukuba, Japan, (2)Natl Res Inst Earth Science, Tsukuba Ibaraki, Japan, (3)NIED, Tsukuba, Japan, (4)OYO Corporation, Tokyo, Japan, (5)OYO Corporation, Tsukuba, Japan, (6)KOKUSAI KOGYO CO., LTD, Tokyo, Japan, (7)ITOCHU Techno-Solutions Corporation, Chiyoda-ku, Japan
In 2012, we began a project of nationwide Probabilistic Tsunami Hazard Assessment (PTHA) in Japan to support various measures (Fujiwara et al., 2013, JpGU; Hirata et al., 2014, AOGS). The most important strategy in the nationwide PTHA is predominance of aleatory uncertainty in the assessment but use of epistemic uncertainty is limited to the minimum, because the number of all possible combinations among epistemic uncertainties diverges quickly when the number of epistemic uncertainties in the assessment increases ; we consider only a type of earthquake occurrence probability distribution as epistemic uncertainty. We briefly show outlines of the nationwide PTHA as follows; (i) we consider all possible earthquakes in the future, including those that the Headquarters for Earthquake Research Promotion (HERP) of Japanese Government, already assessed. (ii) We construct a set of simplified earthquake fault models, called “Characterized Earthquake Fault Models (CEFMs)”, for all of the earthquakes by following prescribed rules (Toyama et al., 2014, JpGU; Korenaga et al., 2014, JpGU). (iii) For all of initial water surface distributions caused by a number of the CEFMs, we calculate tsunamis by solving a nonlinear long wave equation, using FDM, including runup calculation, over a nesting grid system with a minimum grid size of 50 meters. (iv) Finally, we integrate information about the tsunamis calculated from the numerous CEFMs to get nationwide tsunami hazard assessments. One of the most popular representations of the integrated information is a tsunami hazard curve for coastal tsunami heights, incorporating uncertainties inherent in tsunami simulation and earthquake fault slip heterogeneity (Abe et al., 2014, JpGU). We will show a PTHA along the eastern coast of Honshu, Japan, based on approximately 1,800 tsunami sources located within the subduction zone along the Japan Trench, as a prototype of the nationwide PTHA.

This study is supported by part of the research project on research on evaluation of hazard and risk of natural disasters, under the direction of the HERP of Japanese Government.