Long-period ground motion of M9 megathrust earthquake: Construction of integrated model based on wave physics and fusion of observation and computation

2021 Fiscal Year Final Research Report

• Project/Area Number: 17K01322
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Natural disaster / Disaster prevention science
• Research Institution: The University of Tokyo
• Principal Investigator: Furumura Takashi 東京大学, 地震研究所, 教授 (80241404)
• Project Period (FY): 2017-04-01 – 2022-03-31
• Keywords: 長周期地震動 / 巨大地震 / 深発地震 / 2011年東北地方太平洋沖地震 / 南海トラフ巨大地震

Outline of Final Research Achievements

In order to evaluate the risk of long-period ground motions of M9-scale large earthquakes, the generation process of long-period ground motions of the 2011 off the Pacific coast of Tohoku Earthquake was evaluated from strong motion observation data analysis and seismic wave propagation simulation. During the off Tohoku earthquake, the long-period ground motion level of the Kanto basin becomes smaller than the inland earthquake and the Nankai Trough earthquake, and the cause is the S-wave radiation characteristics of the off Tohoku earthquake and the directional characteristics of the three-dimensional basement structure of the Kanto basin. It was confirmed that Long-period ground motion can be also generated even in deep-focus M8-class earthquakes such as the 2008 Okhotsk Sea Deep Earthquake and the 2015 Ogasawara Earthquake, which are generated from S waves incident on the ground surface at a critical angle, and sP conversion and sS reflected wave generated at large distances.

Free Research Field

地震学

Academic Significance and Societal Importance of the Research Achievements

本研究により、南海トラフ沿いや日本海溝沿いで発生が心配されるM9規模の海溝型の超巨大地震や、太平洋プレート内で発生するM8規模の巨大深発地震による長周期地震動の生成過程が明らかとなり、そして地殻・マントル不均質構造を組み込んだ地震波伝播シミュレーションによる予測手法が確立されたことで、M9超巨大地震のリスク評価と災害軽減に大きく貢献することが期待できる。