[P08] Earthquake physics

[P08-16] Numerical Investigation of Temporal Changes in Repeating Earthquake Behavior Before and After the 2011 Tohoku-Oki Earthquake

*Yuki Watanabe¹, Yoshihiro Kaneko¹, Keisuke Yoshida² (1. Graduate School of Science, Kyoto University, 2. Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University)

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.