Japan Geoscience Union Meeting 2025

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S (Solid Earth Sciences ) » S-CG Complex & General

[S-CG61] Dynamics in mobile belts

Wed. May 28, 2025 1:45 PM - 3:15 PM 103 (International Conference Hall, Makuhari Messe)

convener:Yukitoshi Fukahata(Disaster Prevention Research Institute, Kyoto University), Hikaru Iwamori(Earthquake Research Institute, The University of Tokyo), Kiyokazu Oohashi(National Institute of Advanced Industrial Science and Technology ), Chairperson:Kiyokazu Oohashi(National Institute of Advanced Industrial Science and Technology), Yoshiya Usui(Earthquake Research Institute, the University of Tokyo)

1:45 PM - 2:00 PM

[SCG61-01] Crustal structure factors constraining hypocenter distribution in the eastern part of the 2024 Noto Peninsula earthquake, Japan Sea

*Tetsuo No1, Gou Fujie1, Yasuyuki Nakamura1, Tsutomu Takahashi1, Koichiro Obana1, Tatsuya Ishiyama2, Masaru Ichikawa3, Kenichi Akama3 (1.JAMSTEC, 2.ERI, Univ. of Tokyo, 3.JGI)

Keywords:2024 Noto Peninsula earthquake, Seismic survey, Crustal structure, Multichannel seismic reflection profile, Ocean bottom seismograph, Japan Sea

The aftershocks of the 2024 Noto Peninsula earthquake ( MJ7.6) encompassed 150 km across both land and sea, and various observational studies have been conducted in the offshore area through several research cruises following the earthquake. In this study, we established a survey line across the eastern part of the source region in September 2024 and conducted a multi-channel seismic reflection (MCS) survey and a seismic survey using ocean bottom seismographs (OBSs). Using the results of this new seismic survey and existing studies, we presented the relationship between the source distribution and crustal structure around the eastern edge of the Noto Peninsula earthquake. Our seismic survey line, conducted last summer, had a length of 100 km and was located near the eastern edge of the aftershock zone of the Noto Peninsula earthquake. This survey line was set almost orthogonal to northwest-dipping rectangular source fault model NT2 published by the “Integrated Research Project on Seismic and Tsunami Hazards Around the Sea of Japan". Data acquisition specifications were set to obtain the data on the deep crustal structure associated with the earthquake fault of the Noto Peninsula earthquake. The MCS survey was towed by a streamer cable approximately 5 km long, and shot intervals were set at 50 m, running twice along the same survey line in the same direction. The OBS survey consisted of 40 OBSs installed at intervals of approximately 2 km, with shot intervals of 200 m intervals, with five iterations along the same survey line. Preliminary results show an asymmetric anticline with a west- dipping reverse fault corresponding to NT2, which is also consistent with the aftershock distribution obtained from the OBS observations. Reflectors were also observed in the crust under the western wing of the anticline at traveltimes of approximately 8, 10, and 13 s. However, the aftershock distribution near the survey line shows an extremely low-angle aftershock distribution that branches off the west-dipping distribution into the Toyama Trough. The distribution appears to be caused by a different fault than the west-dipping reverse fault corresponding to NT2. Based on these results, the shortening structure is inferred to differ from NT2, instead formed by a north-dipping reverse fault with a northwest-southeast strike. Thus, the aftershock activity likely corresponds to that fault.