[S22] AM-2

[S22-05] Seismic reflection images of active submarine faults in the 2024 Noto earthquake (M7.6) rupture area

*Jin-Oh Park¹, Hamzeh Mohammadigheymasi¹, Yige Yang¹, Ehsan Jamali Hondori², Ayanori Misawa³, Tetsuo No⁴, Hironori Otsuka⁵ (1. AORI, University of Tokyo, 2. Geoscience Enterprise Inc. (GSE), 3. AIST, 4. JAMSTEC, 5. KOBEC)

A large earthquake (M 7.6) with a reverse fault-type focal mechanism (Japan Meteorological Agency, 2024) occurred on the Noto Peninsula on 1 January 2024. The earthquake rupture extended northeast of the Noto Peninsula and generated a large tsunami, allowing us to speculate on shallow crustal movement near the seafloor due to a deep seismogenic fault. The earthquake source fault, estimated from the aftershock distribution of the January 2024 earthquake (Japan Meteorological Agency, 2024), has a total length of about 150 km from the west coast of the Noto Peninsula to the northeast offshore the Noto Peninsula. It is inferred that part of the ~150 km long fault, as an active submarine fault, could serve as the source of the tsunami in the northeast off the Noto Peninsula.During the R/V Hakuho-maru cruise (4-16 March 2024), we conducted a multichannel seismic (MCS) reflection survey to obtain a high-resolution image of the shallow crustal structure containing the active faults in the 2024 Noto earthquake (M7.6) rupture area off the northeast coast of Noto Peninsula. We acquired good quality MCS data on a total of 14 survey lines (~45 km long for each line). We used two GI guns (~12 liters) with a shot interval of 18.75 meters to obtain a high-resolution image of the shallow structure of the active faults. We recorded MCS data with a 5 or 6 second recording length and 2 msec sampling interval using a 1,200 m long, 48 channel streamer with 25 m group spacing. The Trigger Fish 2D navigation data was stored in the UKOOA P1/90 and P2/91 formats. After applying the UKOOA P1/90 navigation data to the MCS data for geometry setting, a series of conventional techniques were applied including trace editing, pre-filtering, spherical divergence correction, de-ghosting, surface-related multiple elimination, predictive deconvolution, stacking velocity analysis, normal moveout correction, common midpoint (CMP) stacking, and Kirchhoff post-stack time migration.Combining the MCS data with sub-bottom profiling (SBP) and multibeam echo sounder (MBES) data, we found a 1 to 2 km wide, ~40 km long, highly deformed zone composed of active reverse and strike-slip faults, close to F43 of the MLIT fault model. Some of the active faults extending near the seafloor develop in the 2024 coseismic rupture area derived from the tsunami waveform inversion, suggesting their tsunamigenic behavior. We identified another active reverse fault near the northeastern F42 of the MLIT fault model. The hanging wall of the reverse fault is intensely uplifted and deformed and contains slope failure structures, probably due to the repeated activity of the fault. In this talk we will present the geological interpretation of the MCS profiles, focusing on the shallow crustal structures that contain the active faults.