Evaluation of earthquake rupture process at the Nankai Trough by integrated method of fault material analysis and numerical simulation

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K04039
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 17040:Solid earth sciences-related
• Research Institution: Osaka University
• Principal Investigator: Hirono Tetsuro 大阪大学, 理学研究科, 准教授 (70371713)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: 南海トラフ地震 / 動力学 / 断層

Outline of Final Research Achievements

Dynamic rupture simulations using reported friction datasets measured in fault rocks on the Nankai Trough, that was ruptured during the 1944 Mw8.0 Tonankai earthquake, were performed. A steady-state friction triggered large slip (about 30 m) near the trench, whereas a high friction suppressed the rupture. The environmental condition in which the pore-fluid pressure was nearly equal to the lithostatic stress decreased the slip about 25 m in case of low friction. However, in case of high friction with negative stress drop, the slip reached about 20 m because the low shear strength did not arrest the inertial motion of rupture propagation. Such differences in fault-rock properties and fluid conditions may fundamentally influence on the complexity and the variability of rupture propagation along the Nankai trough.

Free Research Field

地球物理学

Academic Significance and Societal Importance of the Research Achievements

来たる南海トラフ地震での破壊伝播過程の事前把握のため、地震時における海溝底付近のプレート境界断層の滑り量の定量的評価が重要である。統合国際深海掘削計画で採取された断層試料の分析と実測値を用いた動力学シミュレーションの結果、海溝付近の滑り量は断層の摩擦係数と初期の間隙水圧の状態に依存し、かつ、それらの僅かな差によって大きく変化することが明らかになった。これは、南海トラフ全体の地震時の滑り量の事前評価には、海溝に並行な方向での断層の物質科学特徴の評価が不可欠であることを示唆する。