講演情報
[P08-16]2011年東北沖地震前後に変化した繰り返し地震挙動の数値シミュレーション的検討
*渡邊 悠樹1、金子 善宏1、吉田 圭佑2 (1. 京都大学理学研究科、2. 東北大学理学研究科 地震・噴火予知研究観測センター)
Repeating earthquakes serve as sensitive probes of evolving fault strength, loading, and hieratical fault structure (e.g., Uchida and Burgmann, 2019). High-resolution catalogs reveal that several well-characterized repeaters along the Japan Trench, which ruptured with nearly constant moment magnitude (Mw) and recurrence interval before the Mw 9.0 2011 Tohoku-Oki earthquake, experienced an immediate post-mainshock jump in both Mw and frequency (Yoshida & Ide, 2025). These repeaters decayed over subsequent years, and rupture style temporarily shifted from single to mixed (doublet) events before reverting to single-event dominance (Yoshida & Ide, 2025). To elucidate the underlying physics, we perform 3-D fully dynamic earthquake-cycle simulations (Lapusta & Liu, 2009) that include velocity-weakening patches within a creeping megathrust governed by rate-and-state friction. A systematic parameter search yields a baseline model reproducing the pre-2011 Mw and recurrence intervals of the target repeaters. We then introduce a transient increase in shear loading, mimicking afterslip triggered by the Tohoku-Oki rupture. Our results demonstrate that a model consisting of simple hierarchical velocity-weakening patches, in which an unstable patch is surrounded by a conditionally unstable patch, can reproduce the observed complex behavior of the repeating earthquakes. Before the increase in shear loading, only simple repeaters involving the unstable patch occur. After the loading increases, the surrounding conditionally unstable patch becomes seismically active, resulting in more frequent and higher-magnitude events that are consistent with observations. We will present our ongoing efforts to identify the key physical parameters governing the characteristics and temporal evolution of the target repeating earthquakes.