[S-SS10] 地震発生の物理・断層のレオロジー

[SSS10-17] Multi-Fault Segment Complexity and Multi-Rupture Episodes during the 2024 Mw 7.5 Noto Peninsula Earthquake

*榎本 倫太郎¹、金子 善宏¹、唐 啓賢²、福島 洋²、後藤 浩之³、宮崎 真一¹ (1.京都大学大学院理学研究科、2.東北大学災害科学国際研究所、3.京都大学防災研究所)

キーワード：2024 Noto Peninsula earthquake、Finite fault model、Complex rupture propagation、Ground motion、Earthquake swarm

Major intraplate earthquakes pose a substantial threat to nearby inhabited regions, but their rupture characteristics are often unclear due to limited observations. The 2024 Mw 7.5 Noto Peninsula earthquake in Japan, recorded by numerous near-fault strong-motion seismometers, high-rate GNSS, and satellite data, presents a unique opportunity to investigate fault rupture evolution and the resulting strong ground motions in detail. Using kinematic rupture modeling, we developed a source model that reproduces SAR-based and GNSS data, as well as near-fault velocity and displacement waveforms with periods longer than 4 seconds. Our approach integrates 3D velocity and inelastic attenuation models for Japan, incorporating regional topography and bathymetry. To reduce the number of unknown parameters, we used an a priori fault slip model derived from SAR and GNSS data and fixed the fault geometry and final slip distribution, adjusting only the rupture timing and rise time of individual fault segments. The preferred source model reveals multiple slip episodes and intricate rupture evolution, including a backward-propagating rupture toward the mainshock hypocenter likely triggered by abrupt changes in local fault geometry. The mainshock hypocenter and subsequent rupture initiations occur in areas of increased shear stresses along the periphery of the preceding swarm activity. These subsequent ruptures propagated bilaterally along southwestern and northeastern fault segments with rupture speeds ranging from 1.4 to 2.1 km/s, slower than those of other intraplate thrust earthquakes of similar magnitude. The southwestward rupture broke large slip asperities (up to ~10 m) on non-planar fault segments offshore Monzen, where the coseismic uplift was ~4 m. Our results suggest that the 2024 Noto Peninsula earthquake is a remarkable example of a complex intraplate earthquake involving multi-segment rupture with multiple slip episodes, providing important insights into the physics of rupture propagation and the resulting ground motions.