Japan Geoscience Union Meeting 2023

Presentation information

[J] Online Poster

H (Human Geosciences ) » H-DS Disaster geosciences

[H-DS06] Tsunami and tsunami forecast

Wed. May 24, 2023 10:45 AM - 12:15 PM Online Poster Zoom Room (9) (Online Poster)

convener:Satoko Murotani(National Museum of Nature and Science), Toshitaka Baba(Graduate School of Science and Technology, Tokushima University)

On-site poster schedule(2023/5/23 17:15-18:45)

10:45 AM - 12:15 PM

[HDS06-P16] Characterized earthquake fault models and tsunami simulations for probabilistic tsunami hazard assessment integrating 5 regions in Japan.

*Koichi Murata1, Kenji Hirata2, Hiroyuki Fujiwara2, Hiromitsu Nakamura2, Nobuyuki Morikawa2, DOHI YUJI2, Makoto Nemoto1, Tadashi Kito1, Xuelei Zhang1, Yasuhiro Murata3, Mariko Korenaga4, Yuta Abe4 (1.OYO Corporation, 2.NIED (National Research Institute for Earth Science and Disaster Resilience), 3.KOKUSAIKOGYO CO., LTD., 4.CTC (ITOCHU Techno-Solutions Corporation))

Keywords:Characterized fault model, Long-term evaluation, Probabilistic tsunami hazard assessment

A probabilistic tsunami hazard assessment (PTHA) of tsunamis associated with earthquakes occurring along five subduction zones around Japan (the Kurul Trench, the Japan Trench, the Sagami Trough, the Nankai Trough, and the Ryukyu Trench) was conducted based on five long-term assessments published by the Headquarters for Earthquake Research Promotion (HERP) (Hirata et al., this conference). For your information, Dohi et al. (2022, JAEE) estimated the PTHA integrating the four regions along the Kuril Trench, the Japan Trench, the Sagami Trough, and the Nankai Trough.
The 5-region integrating PTHA consists of three main components: the construction of earthquake fault models, tsunami simulations, and the analysis of hazard curves. In this study, we focus on the construction of ‘characterized earthquake fault models’ (CEFMs) for the earthquakes evaluated by the HERP and also report the result of tsunami simulations. For the analysis of hazard curves, please refer to Ohno et al. (this conference).
CEFMs were constructed based on the long-term assessment of the HERP. However, scientific knowledge of seismic activity along the Ryukyu Trench is lacking, and except for a few areas, almost nothing has been evaluated in the long-term assessment. Therefore, we constructed CEFMs of along the Ryukyu Trench as "earthquakes whose epicenters are difficult to identify in advance".
The procedure of setting up CEFMs for interplate earthquakes is the following. First, elemental faults (approx. 5 km square) were laid out on the upper surfaces of the subducting Pacific Plate and the Philippine Sea Plate. Next, the CEFM was constructed as a set of elemental faults. A CEFM consists of three different slip areas: “background slip area”, “large slip area” (LSA), and “super-large slip area” (SLSA). The existence of the SLSA and the slip amount and the area of the LSA and the SLSA were set with reference to " Tsunami prediction method for earthquakes with characterized source faults (Tsunami Recipe)" (HERP, 2017). For an earthquake source area, several to tens CEFMs were constructed so as to have the LSA in various locations each CEFM, in which LSAs are placed at approximately half pitch intervals. The aspect ratio of the LSA and the SLSA is set to approximately two, and the overlap ratio between neighboring LSAs is approximately 50%. However, along the Ryukyu Trench, CEFMs were set as square-shaped faults as long as the fault plane is not constrained by the area and not set the SLSA. For intraplate earthquakes, CEFMs were set as a single rectangular fault.
The CEFM settings for each region are as follows. For the Kuril Trench, seven types were set: “Megaquakes (17th century type)” (Mw8.6-9.2), “Interplate great earthquakes” (Mw7.7-8.8), “Smaller interplate earthquakes” (Mw7.0-7.8), “Tsunami earthquakes” (Mt7.8-8.2), “Slightly shallower intraplate earthquakes” (Mw8.3-8.5), “Slightly deeper intraplate earthquakes” (Mw7.6-8.0), and “outer-rise earthquakes” (Mw8.1-8.3). For the Japan Trench, seven types were set: “Megaquakes (off the Pacific coast of Tohoku type)” (Mw8.6-9.2), “Interplate great earthquakes” (Mw7.7-8.8), “Smaller interplate earthquakes” (Mw6.8-7.8), “Tsunami earthquakes” (Mt8.6-9.0), “Slightly shallower intraplate earthquakes” (Mw7.0-7.7 and Mw8.3-8.5), “Slightly deeper intraplate earthquakes” (Mw7.0-7.7), and “outer-rise earthquakes” (Mw8.1-8.3). For the Sagami Trough, two types were set: ”M8 class earthquakes” (Mw7.9-8.6), and “M7 class earthquakes” (Mw6.8-7.8). For the Nankai Trough, Mw 7.6-9.0 were set. For the Ryukyu Trench, Mw 7.0-9.4 were set. The number of CEFMs were approx. 5,000 for the Kuril Trench, approx. 4,000 for the Japan Trench, approx. 1,000 for the Sagami Trough, approx. 3,000 for the Nankai Trough, and approx. 5,000 for the Ryukyu Trench. Thus, the total number of CEFMs were approx. 17,000 for the five regions.
This study is conducted as a part of the research project “Research on the hazard and risk assessment” at NIED.