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[SSS12-P12] The delayed Aftershock Activity associated with the 2024 Noto Peninsula Earthquake
Keywords:Aftershock, Afterslip, 2024 Noto Peninsula Earthquake
On 1 January 2024, an earthquake with a Japan Meteorological Agency (JMA) magnitude (Mj) of 7.6 struck the northern coast of the Noto Peninsula. The fault rupture during the earthquake extended for 150 km along the shoreline of the northern edge of the Noto Peninsula (e.g., HERP, 2024). The focal mechanism indicated a reverse fault motion striking NE–SW and dipping SE.
According to the Japan Sea Earthquake and Tsunami Research Project model (JSPJ model), seven fault segments are located along the northern edge of the Noto Peninsula. The two northeast segments dip to the northwest, while the five segments to the southwest of the mainshock dip to the southeast. Fujii and Satake (2024) have reported that the northeastern segments caused almost no slip associated with the earthquake sequence based on a tsunami simulation with the JSPJ model. Yang et al. (2024) have also proposed that the east fault segment caused a very small coseismic slip that was accompanied by significant afterslip movements. However, Xu et al. (2024) and Ma et al. (2024) have concluded that the fault segments to the east of the hypocenter ruptured, in contrast to the research results reported by Fujii and Satake (2024).
The presentation of these variety models for the rupture behavior of the multisegment rupture of the earthquake implies that understanding of the properties of the earthquake is incomplete. The geodesy data—GNSS and InSAR data—have been insufficient to provide detailed information about the earthquake because the hypocenter and seismic sequence region were located on the edge and offshore regions of the peninsula. We therefore needed to precisely analyze the aftershocks, which could provide important information needed to understand the behavior of the earthquake. In this study, we focused on the spatiotemporal distribution of the aftershocks of the earthquake to elucidate the processes by which the earthquake ruptured.
A few hours after the mainshock, aftershocks spread throughout the entire fault rupture zone in the JSPJ model. The first aftershock (Mj 5.7) occurred two minutes after the mainshock and was located near the NT9 segment, which is the segment farthest from the mainshock. More than 60 aftershocks occurred within the first hour across the entire fault rupture zone. The first aftershock (Mj 4.3) in northeastern segment occurred near the NT3 segment about 30 minutes after the mainshock. There was a clear delay in the occurrence of aftershocks in the eastern segments (NT2 to NT4) relative to those in the western segments (NT6, NT8, and NT9).
Yang et al. (2024) have reported that the early afterslip and a slighttransfer of stress caused aftershocks in the northeastern regions after the 2024 Noto earthquake. Furthermore, there was no significant slip on the northeastern segments during the mainshock. The delayed aftershock activity in the northeastern segments, which was discovered in this study, may consequently have influenced by the subsequent early afterslip rather than the dynamic rupture of the mainshock. In other words, the northeastern segments may not have caused a cosesimic rupture. This interpretation is consistent with the result of a tsunami simulation that assumed almost no coseismic slip on the northeastern segments, NT2 and NT3 (Fujii and Satake, 2024).
Few studies have focused on delayed aftershock activity (Yin et al., 2018; Jiang et al., 2021), but conducting precise spatiotemporal analyses of aftershocks is crucial for estimating source fault models and understanding the behavior of multisegment ruptures.
According to the Japan Sea Earthquake and Tsunami Research Project model (JSPJ model), seven fault segments are located along the northern edge of the Noto Peninsula. The two northeast segments dip to the northwest, while the five segments to the southwest of the mainshock dip to the southeast. Fujii and Satake (2024) have reported that the northeastern segments caused almost no slip associated with the earthquake sequence based on a tsunami simulation with the JSPJ model. Yang et al. (2024) have also proposed that the east fault segment caused a very small coseismic slip that was accompanied by significant afterslip movements. However, Xu et al. (2024) and Ma et al. (2024) have concluded that the fault segments to the east of the hypocenter ruptured, in contrast to the research results reported by Fujii and Satake (2024).
The presentation of these variety models for the rupture behavior of the multisegment rupture of the earthquake implies that understanding of the properties of the earthquake is incomplete. The geodesy data—GNSS and InSAR data—have been insufficient to provide detailed information about the earthquake because the hypocenter and seismic sequence region were located on the edge and offshore regions of the peninsula. We therefore needed to precisely analyze the aftershocks, which could provide important information needed to understand the behavior of the earthquake. In this study, we focused on the spatiotemporal distribution of the aftershocks of the earthquake to elucidate the processes by which the earthquake ruptured.
A few hours after the mainshock, aftershocks spread throughout the entire fault rupture zone in the JSPJ model. The first aftershock (Mj 5.7) occurred two minutes after the mainshock and was located near the NT9 segment, which is the segment farthest from the mainshock. More than 60 aftershocks occurred within the first hour across the entire fault rupture zone. The first aftershock (Mj 4.3) in northeastern segment occurred near the NT3 segment about 30 minutes after the mainshock. There was a clear delay in the occurrence of aftershocks in the eastern segments (NT2 to NT4) relative to those in the western segments (NT6, NT8, and NT9).
Yang et al. (2024) have reported that the early afterslip and a slighttransfer of stress caused aftershocks in the northeastern regions after the 2024 Noto earthquake. Furthermore, there was no significant slip on the northeastern segments during the mainshock. The delayed aftershock activity in the northeastern segments, which was discovered in this study, may consequently have influenced by the subsequent early afterslip rather than the dynamic rupture of the mainshock. In other words, the northeastern segments may not have caused a cosesimic rupture. This interpretation is consistent with the result of a tsunami simulation that assumed almost no coseismic slip on the northeastern segments, NT2 and NT3 (Fujii and Satake, 2024).
Few studies have focused on delayed aftershock activity (Yin et al., 2018; Jiang et al., 2021), but conducting precise spatiotemporal analyses of aftershocks is crucial for estimating source fault models and understanding the behavior of multisegment ruptures.