[S-CG55] Dynamics in mobile belts

[SCG55-14] Characteristics of focal mechanism solutions prior to the 2024 Noto Peninsula Earthquake (M7.6) and its implication for heterogeneous stress field

*Satoshi Matsumoto¹, Kentaro Emoto¹, Shungo Tasa², Shinichi Sakai³ (1.Institute of Seismology and Volcanology, Faculty of Sciences, Kyushu University, 2.Graduate School of Science, 3.Interfaculty Initiative in Information Studies, The University of Tokyo)

Keywords:The 2024 Noto Peninsula Earthquake, Focal mechanism, Dense seismic network, Stress field

The 2024 Noto Peninsula Earthquake (M7.6) occurred on January 1^st heavily damaged people and residences and is associated subsequent high aftershock activity. Before the mainshock, earthquake swarm including large earthquake with M6.5 has started since 2020. In order to obtain information about stress field in the area, we deployed temporal seismic station from August 2022. Over 23000 events detected for about one year and about a few hundreds focal mechanisms determined. Generally, P-axis oriented in NW – SE direction with reverse fault type focal mechanisms. Unfortunately, region where we can deploy station is restricted due to peninsula topography, It is difficult to derive enough number of focal mechanisms for discussion stress field. Therefore, we performed composite focal mechanism estimation at blocks spatially divided in the target area. The result shows that P-axes in western part of hypocentral area rotate counter clockwise from eastern part. This suggests that stress field in eastern part where M6.5 occurred is different from one in western part. In addition, After occurrence of M6.5 event, stress field in eastern shallow part changed to strike slip regime from reverse fault one. These spatially and temporally heterogeneous stress field may cause complex rupture propagation of the M7.6 main shock.