Geomechanical interpretation of the generation of sticking zones and slip in the decolma zone of the trench-subducting plate

2023 Fiscal Year Final Research Report

• Project/Area Number: 21H01427
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 22030:Geotechnical engineering-related
• Research Institution: Kobe University
• Principal Investigator: Iizuka Atsushi 神戸大学, 都市安全研究センター, 名誉教授 (40184361)
• Co-Investigator(Kenkyū-buntansha): 橘 伸也 神戸大学, 工学研究科, 教授 (90432567)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 地盤力学 / デコルマ帯 / 弾塑性材料 / 鉱物変質 / 境界値問題

Outline of Final Research Achievements

In this research project, we use nonlinear elastoplastic theory to interpret the mechanical property changes associated with the alteration of the decolma zone at the oceanic plate surface during trench slip and to explain the generation of a sticking zone and the mechanism of slow slip of a plate boundary fault as a soil-water coupled boundary value problem. The following three issues are considered in this study: (1) elasto-plastic constitutive theory of mechanical property changes associated with the alteration of smectite minerals to illite in the Decoulema zone, (2) consideration of the dehydration field from within smectite minerals during their alteration to illite as a governing equation, (3) nonlinear elastoplastic constitutive theory and the initial value boundary value problem as a coupled field between pore water generation and movement, and the analysis of this problem.

Free Research Field

地盤工学

Academic Significance and Societal Importance of the Research Achievements

本課題は，海洋プレート表層部のデコルマ帯の海溝部滑り込み時の変質に伴う力学特性変化を非線形弾塑性理論によって解釈し，プレート境界断層の固着域の生成やゆっくり滑りのメカニズムを土・水連成境界値問題として説明することにより、地震学への地盤力学の積極的な貢献を果たそうとしている．スロースリップ現象自体は揺れを発生させることはないが，断層試料を用いた室内試験結果から，スロースリップ現象が生じていた領域が地震時に高速で滑ることで地震を巨大化させる可能性が考えられており，発生メカニズムの解明が急がれている．