[U-15] The 2024 Noto Peninsula Earthquake (1:J)

[U15-P52] Shear wave splitting and seismic velocity structure in the focal area of the 2024 M7.6 Noto Peninsula earthquake, central Japan

*Tomomi Okada¹, Martha Savage², Ryota Takagi¹, Keisuke Yoshida¹, Satoshi Matsumoto³, Kentaro Emoto³, Yoshiko Yamanaka⁴, Kei Katsumata⁵, Takuto Maeda⁶, Motoko Ishise⁷, Shinichi Sakai⁸, Masatoshi Miyazawa⁹, Toshiko Terakawa⁴, Mako Ohzono⁵, Hiroshi Yakiwara¹⁰, Kazutoshi Imanishi¹¹, Naoki Uchida¹, Ayaka Tagami¹, Ryotaro Fujimura¹, Satoshi Hirahara¹, Shuutoku Kimura¹, Takuo Shibutani⁹, Hiroyuki Noda⁹, Tomoaki Nishikawa⁹, Airi Nagaoka⁹, Yuki Funabiki⁹, Yoshihiro Hiramatsu¹² (1.Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 2.Victoria University of Wellington, New Zealand, 3.Kyushu University, 4.Nagoya University, 5.Hokkaido University, 6.Hirosaki University, 7.Yamagata University, 8.University of Tokyo, 9.Kyoto University, 10.Kagoshima University, 11.National Institute of Advanced Industrial Science and Technology, 12.Kanazawa University)

On January 1, 2024, an M7.6 Noto Peninsula earthquake occurred in the northern Noto Peninsula and the offshore east of the Noto Peninsula, extending about 150 km. In our previous study (Okada et al., 2024, doi: 10.1186/s40623-024-01974-0) on the preceding earthquake swarm area, the results of the S-wave splitting analysis indicated that the southern part of the earthquake swarm source region shows anisotropy due to stress, and the northern part shows anisotropy due to structures such as faults, indicating that structures such as faults are more developed and seismic activity is more active in the northern part. On the other hand, in the southern part of the earthquake swarm epicenter region, a large P- and S-wave velocity ratio was observed in the southern part of the epicenter region. Old magma reservoir and overpressured fluid were thought to cause the high Vp/Vs, suggesting a relationship between seismic activity and fluids in this region. Based on the results of Okada et al. (2024), we examine the relationship between S-wave splitting analysis and seismic wave velocity structure in the Noto Peninsula earthquake source region using temporal observation data and the Noto Peninsula earthquake.
S-wave splitting analysis using MFAST (Savage et al., 2010) shows that after the 2024 Noto Peninsula earthquake, anisotropy due to stress was generally observed in the source region. Note that in the area of seismic swarms until 2023, aftershocks occurred in the southern part of the epicenter, where stress anisotropy was observed. On the other hand, structural anisotropy was also observed in some areas of the western part of the source region, possibly reflecting faulting and other structures.
The seismic wave velocity structure obtained by Zhang and Thurber (2003, 2006) indicates that the main shock of the M7.6 Noto Peninsula earthquake was located near a high Vp/Vs region, which was estimated to be an old magma reservoir. This indicates that fluids such as water are also involved in the occurrence of the M7.6 Noto Peninsula earthquake.