[S-GD02] Crustal Deformation

[SGD02-P10] Extreme coseismic uplift and faulting complexity during the January 1, 2024, M_w 7.5 Noto Peninsula earthquake

*Chi-Hsien Tang¹, Yo Fukushima¹, Shinji Toda¹, Keisuke Yoshida², Naoya Takahashi², Takayuki Takahashi¹ (1.International Research Institute of Disaster Science, Tohoku University, 2.Graduate School of Science, Tohoku University)

Keywords:Noto Peninsula earthquake, Crustal deformation, Coseismic slip, Dislocation model, GNSS, SAR

On the first day of 2024, a once-in-a-thousand-year M_w 7.5 earthquake struck the Noto Peninsula in Ishikawa Prefecture and triggered a tsunami of up to 1.2 m at Wajima. The mainshock was located in the NE part of the peninsula at a depth of 16 km, and the aftershocks exhibit a bilateral migration to the NE and SW, with a total span of more than 150 km. The focal mechanism and aftershock distribution suggest that the earthquake primarily occurred on a NE-SW-striking, SE-dipping thrust fault, and may also trigger the activity of some nearby secondary faults. GNSS data, SAR images, and coastal uplift measurements show coseismic uplift of 1-4 m along the NW coastline of the peninsula. If the earthquake is characteristic, its recurrence interval can be roughly estimated to be 1-4 kyr, given that the maximum uplift rate of the peninsula is 1 m/kyr. In addition, the WSW horizontal coseismic displacements of 1-2 m indicate a certain contribution of right-lateral strike-slip faulting. To understand the complex faulting during the 2024 Noto Peninsula earthquake, we performed joint kinematic inversion of GNSS, pixel offsets of ALOS-2, and coastal uplift data to explore the coseismic slip distribution. We used the mapped active faults offshore the peninsula and 15-day relocated aftershocks as guides for constructing the fault geometry. The inverted coseismic slip model suggests that there were three ruptured asperities during the mainshock. Two asperities occurred near the mainshock, one in the NE and the other in the SW, with an estimated moment release of each equivalent to M_w 7.0. The southwestward propagation of the rupture eventually broke the third asperity near Wajima. The third ruptured asperity is characterized by the maximum right-lateral and thrust slip of ~6 and ~8 m, respectively, with the corresponding moment release equivalent to M_w 7.2. The total geodetic moment magnitude of the coseismic slip is about M_w 7.5, which is in good agreement with the seismic moment magnitude. The 2024 Noto Peninsula earthquake reminds us of the seismic potential and risk posed by intraplate thrust faults, which can be interseismically locked and remain nearly quiescent for long periods before the eventual failure.