[S-SS10] 地震発生の物理・断層のレオロジー

[SSS10-18] 地震計ノードを用いた高密度観測に基づく2024年能登半島地震陸域震源域の詳細なS波速度構造

*高木 涼太¹、吉田 圭佑¹、岡田 知己¹、福島 駿¹、宮澤 理稔²、前田 拓人³、平野 史朗³、石瀬 素子⁴、椎名 高裕⁵、平松 良浩⁶ (1.東北大学大学院理学研究科附属地震・噴火予知研究観測センター、2.京都大学防災研究所、3.弘前大学大学院理工学研究科、4.山形大学理学部、5.産業技術総合研究所、6.金沢大学理工研究域地球社会基盤学系)

キーワード：能登半島地震、群発地震、S波速度構造、地震計ノード、高密度地震観測、常時微動表面波トモグラフィー

The sequence of the preceding swarm, the Mw 7.5 mainshock, and its aftershocks in the Noto Peninsula exhibits complex spatial distributions of fault behavior. To identify the factors controlling this complexity, we conducted dense nodal seismic observations in the onshore focal area of the Noto earthquake. The observations were carried out in two periods: the first from October to November 2023 with 12 nodes, and the second from July to November 2024 with 21 nodes. The node separation is ~5 km. We applied ambient noise surface wave tomography to the dense seismic data to image detailed S-wave velocity structure beneath the Noto Peninsula. The multicomponent cross-correlation functions of ambient noise extracted Rayleigh and Love waves in 0.05–0.5 Hz, and the extracted Rayleigh and Love waves constrained the S-wave velocity structure in the 0–25 km depth range. The preliminary results show the spatial correlation between the S-wave velocity structure and the distribution of coseismic uplift. In the 5–10 km depth, we found two high-velocity anomalies along the northern coast of the Noto Peninsula. The high-velocity anomalies are located where the coastlines protrude seaward, coinciding with the two peaks of the coseismic uplift. The swarm earthquakes and aftershocks tend to avoid the high-velocity anomalies. The results suggest that the structural heterogeneity controls the occurrence style of the preceding swarm, the Mw7.5 earthquake, and its aftershocks.