[S-SS10] Fault Rheology and Earthquake Physics

[SSS10-18] Detailed S-wave velocity structure in the onshore focal area of the 2024 Noto earthquake revealed by dense nodal seismic observations

*Ryota Takagi¹, Keisuke Yoshida¹, Tomomi Okada¹, Shun Fukushima¹, Masatoshi Miyazawa², Takuto Maeda³, Shiro Hirano³, Motoko Ishise⁴, Takahiro Shiina⁵, Yoshihiro Hiramatsu⁶ (1.Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 2.Disaster Prevention Research Institute, Kyoto University, 3.Graduate School of Science and Technology, Hirosaki University, 4.Faculty of Science, Yamagata University, 5.National Institute of Advanced Industrial Science and Technology, 6.School of Geosciences and Civil Engineering, Kanazawa University)

Keywords:Noto earthquake, Swarm, S-wave velocity structure, Seismic node, Dense seismic observation, Ambient noise surface wave tomography

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.