5:15 PM - 6:45 PM
[U15-P11] Generation Process of the 2024 Mw7.5 Noto Peninsula earthquake Inferred from Microearthquake Migration that Continued for a Few Years on the Fault
Keywords:2024 Noto Peninsular Earthquake, Preceding Earthquake Swarm, Earthquake Migration, Fluid Migration, Aseismic Slip Propagation
At 16:10 on January 1, 2024 (JST), an Mw 7.5 reverse-fault earthquake occurred around the northern Noto Peninsula. In the area surrounding this hypocenter, an intense earthquake swarm had occurred since the end of 2020, with an Mw5.2 earthquake in June 2022 and an Mw6.2 earthquake in May 2023 in the shallow extension of the same fault (Yoshida et al., 2023 JGR, 2023 GRL). The occurrences of upward earthquake migration and aseismic slip and fault opening (Nishimura et al., 2023) suggest that crustal fluid movement was involved in this sequence. In this study, we investigate the spatio-temporal variations of microearthquakes to understand the generation process of the Mw7.5 earthquake.
We relocated the hypocenters of earthquakes listed in the JMA unified catalog from 2003 to January 31, 2024. We first examined the observed waveforms of the Mw7.5 earthquake and the two preceding earthquakes and then modified the arrival times listed in the catalog.
The obtained results show that most of the earthquakes in the last 100 days, including those that became active within a day of the 2024 Mw7.5 earthquake, occurred on the same fault (hereafter, Mw5.2 earthquake fault) as the 2022 Mw5.2 and 2023 Mw6.2 earthquakes. Furthermore, some aftershocks of the Mw7.5 earthquake occurred on the same fault, suggesting that the Mw7.5 earthquake was initiated on the Mw5.2 earthquake fault and that a large slip also occurred on the same fault. Although previous studies have reported that a series of seismicity occurred in multiple clusters more than a few kilometers apart, we found that many of the earthquakes can also be explained as slips on the same fault. The aseismic slip reported in the previous study is also located in the deep extension of the same fault, suggesting that many of the activities (Mw6.2, Mw5.2, and at least part of Mw7.5 earthquakes, microearthquakes, and aseismic slip) may have occurred on the same continuous fault zone. Still, aftershocks are also distributed on a plane conjugate to the Mw5.4 fault in the eastern part and are also concentrated on a plane a few km shallower than the Mw5.2 fault in the central part, suggesting that the mainshock rupture also occurred on planes different from the Mw5.2 fault.
It has been reported that westward microearthquake migration has occurred on the Mw5.2 earthquake fault since 2021 (Yoshida et al., 2023, JGR). Our results obtained by extending the analysis period indicate that westward migration continued on the fault after the 2022 Mw5.2 earthquake and intense seismicity immediately before the Mw7.5 earthquake occurred near the western edge. The locations of preceding earthquakes are also directly above the cluster where the previous study indicated the occurrence of earthquake migration from deep to shallow areas via multiple planes. These earthquakes reached the east of the source region of the 1729 Mw6.6-6.9 earthquake. Large surface displacements were observed above this region immediately after the Mw7.5 mainshock, suggesting that a large coseismic slip occurred there. The preceding earthquakes, including the Mw>5 events a few minutes and a few seconds before the mainshock, may have triggered the slip at the asperity of the 1729 earthquake, which further propagated to the west and east, rupturing different fault planes as well, producing the mainshock rupture extending approximately 150 km.
We relocated the hypocenters of earthquakes listed in the JMA unified catalog from 2003 to January 31, 2024. We first examined the observed waveforms of the Mw7.5 earthquake and the two preceding earthquakes and then modified the arrival times listed in the catalog.
The obtained results show that most of the earthquakes in the last 100 days, including those that became active within a day of the 2024 Mw7.5 earthquake, occurred on the same fault (hereafter, Mw5.2 earthquake fault) as the 2022 Mw5.2 and 2023 Mw6.2 earthquakes. Furthermore, some aftershocks of the Mw7.5 earthquake occurred on the same fault, suggesting that the Mw7.5 earthquake was initiated on the Mw5.2 earthquake fault and that a large slip also occurred on the same fault. Although previous studies have reported that a series of seismicity occurred in multiple clusters more than a few kilometers apart, we found that many of the earthquakes can also be explained as slips on the same fault. The aseismic slip reported in the previous study is also located in the deep extension of the same fault, suggesting that many of the activities (Mw6.2, Mw5.2, and at least part of Mw7.5 earthquakes, microearthquakes, and aseismic slip) may have occurred on the same continuous fault zone. Still, aftershocks are also distributed on a plane conjugate to the Mw5.4 fault in the eastern part and are also concentrated on a plane a few km shallower than the Mw5.2 fault in the central part, suggesting that the mainshock rupture also occurred on planes different from the Mw5.2 fault.
It has been reported that westward microearthquake migration has occurred on the Mw5.2 earthquake fault since 2021 (Yoshida et al., 2023, JGR). Our results obtained by extending the analysis period indicate that westward migration continued on the fault after the 2022 Mw5.2 earthquake and intense seismicity immediately before the Mw7.5 earthquake occurred near the western edge. The locations of preceding earthquakes are also directly above the cluster where the previous study indicated the occurrence of earthquake migration from deep to shallow areas via multiple planes. These earthquakes reached the east of the source region of the 1729 Mw6.6-6.9 earthquake. Large surface displacements were observed above this region immediately after the Mw7.5 mainshock, suggesting that a large coseismic slip occurred there. The preceding earthquakes, including the Mw>5 events a few minutes and a few seconds before the mainshock, may have triggered the slip at the asperity of the 1729 earthquake, which further propagated to the west and east, rupturing different fault planes as well, producing the mainshock rupture extending approximately 150 km.