2011年東北地方太平洋沖地震では、これまで地震時断層すべりが発生しないと考えられていた海溝軸周辺で、50mを超える巨大断層すべりが確認され、各種地球物理学的調査・観測データ、深海掘削、実験、シミュレーションなどにより、地震時の巨大断層すべりのメカニズムが明らかにされてきた。一方で、地震時断層すべりの原因となる「地震前および地震間」の断層固着状態については、東北沖地震や内陸地震での観測データ、理論研究、モデル研究に基づき、「プレート境界浅部では地震後に急激に力学的固着が進行する」という考えと、「プレート境界浅部は力学的に固着しない」という考えが提案されており、統一的な見解はまだ得られていない。そこで、本セッションでは、海溝型巨大地震の震源断層における断層強度の回復や応力蓄積過程がどのように進行するのかという、地震発生プロセスの根幹となる問題に迫ることを目的とする。そのため、世界各地の沈み込み帯における地震発生域を対象に、地球物理学、測地学、地質学、岩石学、地球化学、掘削科学、モデル研究、理論研究など、幅広い分野からの研究発表を歓迎する。

In the 2011 Tohoku-Oki Earthquake, large fault slips exceeding 50 meters were observed near the trench axis, an area previously thought to experience stable sliding or aseismic slip during an earthquake cycle. Various methods, including geophysical surveys, observations, ocean drilling, experiments, and simulations, have been employed to clarify the mechanisms behind these shallow, large fault slips. However, the state of fault locking before and between earthquakes - critical to understanding fault slip - remains unclear. To answer this question based on data from the Tohoku-Oki and inland earthquakes, as well as theoretical and model studies, two contrasting hypotheses have been proposed: one suggests that mechanical locking in the shallow part of the plate boundary rapidly progresses after an earthquake, while the other posits that the shallow part remains mechanically unlocked throughout an earthquake cycle. A unified view on this issue has not yet been established. This session aims to address the fundamental problem in the earthquake generation process: how fault strength recovers and stress accumulates along the source fault of a subduction seismogenic zone. We also hope to use the session as an opportunity to share new knowledge about the geophysical and geological structure of the source faults of megathrust earthquakes, and their spatial variation along and across the subduction zone. We invite research presentations from a wide range of fields, including geophysics, geodesy, geology, petrology, geochemistry, drilling science, and both model and theoretical researches, with a focus on subduction seismogenic zones worldwide.