Inversion method of fault-slip analysis to determine stress tensor and friction coefficient

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K03780
• 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: Kyoto University
• Principal Investigator: Sato Katsushi 京都大学, 理学研究科, 准教授 (70509942)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 応力逆解析 / 小断層解析 / 摩擦係数 / 断層不安定度

Outline of Final Research Achievements

Stress tensor inversion method was improved to determine both stress condition and friction coefficient of faults. Stress condition controls shear stress directions on fault planes, which are expected to be parallel with observed slip directions (Wallace-Bott hypothesis). Observed fault planes are expected to have large fault instability values, which are calculated from both stress condition and friction coefficient. This study combined the above-mentioned two criteria to compose a new objective function of inversion analysis.
The new method was tested by some numerical analyses using artificial fault-slip data. As the result, an improvement of detectability of stress conditions from polyphase fault-slip data was confirmed. The method was applied to outcrop-scale faults cutting Quaternary Sekinan Group in Oita Prefecture. Two normal faulting stresses with N-S tension and ENE-WSW tension axes were obtained (friction coefficient: 0.93 and 0.49, respectively).

Free Research Field

構造地質学

Academic Significance and Societal Importance of the Research Achievements

応力逆解析は構造地質学だけでなく地震学の分野で広く用いられている．本研究により岩石の力学的挙動を決定付けるパラメタである摩擦係数を推定できるようになり，プレート運動などの外力に対する地殻の応答を理解する研究が進むと期待される．例えば地質時代の複雑な応力変遷史の解明や，地震発生条件の非一様性の理解に寄与できるだろう．また，活断層の摩擦係数評価等を行えば，地盤安定性の評価の高精度化にも繋がると期待される．