1:45 PM - 2:00 PM
[U15-01] Seismic activity in the Noto Peninsula and the 2024 M7.6 earthquake
★Invited Papers
Keywords:earthquake swarm, fluid, submarine active fault, aseismic fault movement
On January 1, 2024, an M7.6 earthquake struck the Noto Peninsula, resulting in significant damage from both strong ground motion and tsunami. This study outlines the process leading to the 2024 M7.6 earthquakes, together with the seismotectonics in the Noto Peninsula and the events preceding the M7.6 earthquake.
Off the northern coast of the Noto Peninsula, active faults are segmented into Suzu–oki, Wajima–oki, Saruyama–oki, and Monzen–oki (Inoue and Okamura, 2010). These faults exhibit reverse faulting with southeast dips, uplifting the Peninsula. The eastern half of the Monzen-oki segment is responsible for the source fault of the 2007 M6.9 earthquake. The 1729 M6.6–7.0 earthquake is potentially linked to activity in the Wajima-oki segment (Hamada et al., 2016).
In the northeastern tip of the Noto Peninsula, intense earthquake swarm and transient crustal deformation have been ongoing since December 2020. Swarm activities primarily concentrated in four areas, with earthquakes predominantly occurring along southeast-dipping faults in the western, northern, and eastern regions, and showing normal and strike-slip mechanisms in the southern region at depths deeper than 15 km. Studies have inferred fluid distribution in the deeper southern region (e.g., Okada et al., 2024; Yoshimura et al., 2023).
The spatiotemporal migration of hypocenters conforms to a fluid diffusion model, suggesting that the swarm is likely driven by fluids ascending from deep regions to intrude the southeast-dipping fault zone (e.g., Amezawa et al., 2023; Yoshida et al., 2023a). High He3/He4ratios were observed in hot spring waters near the southern part, indicating the presence of fluid components of deep origin (Kagoshima, et al., 2024).
The M6.5 earthquake on May 5, 2023, occurred at the shallow end of the previously identified source fault in the eastern area, with seismicity significantly extending towards the shallow extension after this earthquake. Precise hypocenter determination revealed discrepancies between the source fault of the M6.5 earthquake and the submarine active faults (Yoshida et al., 2023b; Kato, 2024).
The transient deformation, coinciding with the swarm, is predominantly attributed to slow slip events involving opening and/or reverse faulting on low–angle southeast–dipping faults located in the deeper extension zone of the swarm source areas in the western, northern, and eastern regions (Nishimura et al., 2023). This aseismic fault movement induces stress accumulation on faults within the seismic zone. The increase in stress and the intrusion of fluids into the faults of the seismic zone, prolonging swarm activity (Nishimura et al., 2023).
The hypocenter of the M7.6 event was situated between the aseismic fault and the swarm faults, suggesting that fluid intrusion into faults and stress elevation due to aseismic fault movement may have triggered fault slip around the hypocentral area.
Based on precise hypocenter determination of aftershocks and other data, it is likely that the M7.6 event was caused by the movement of offshore active faults. Aseismic fault movement induces stress buildup on the neighboring Suzu-oki and Wajima-oki segments, potentially facilitating fault rupture on both sides of the hypocenter. Furthermore, stress carried over from the 2007 M6.9 earthquake might have contributed to the westward propagation of fault rupture, ultimately culminating in the M7.6 earthquake.
Various fault models have been proposed for the M7.6 earthquake. Large slip areas were estimated on the shallow parts of the fault planes in the southwest portion of the source region and near the hypocenter, as well as in the northeastern portion of the source region, with the former two resulting in significant coastal uplift and the latter being a major contributor to the tsunami.
Off the northern coast of the Noto Peninsula, active faults are segmented into Suzu–oki, Wajima–oki, Saruyama–oki, and Monzen–oki (Inoue and Okamura, 2010). These faults exhibit reverse faulting with southeast dips, uplifting the Peninsula. The eastern half of the Monzen-oki segment is responsible for the source fault of the 2007 M6.9 earthquake. The 1729 M6.6–7.0 earthquake is potentially linked to activity in the Wajima-oki segment (Hamada et al., 2016).
In the northeastern tip of the Noto Peninsula, intense earthquake swarm and transient crustal deformation have been ongoing since December 2020. Swarm activities primarily concentrated in four areas, with earthquakes predominantly occurring along southeast-dipping faults in the western, northern, and eastern regions, and showing normal and strike-slip mechanisms in the southern region at depths deeper than 15 km. Studies have inferred fluid distribution in the deeper southern region (e.g., Okada et al., 2024; Yoshimura et al., 2023).
The spatiotemporal migration of hypocenters conforms to a fluid diffusion model, suggesting that the swarm is likely driven by fluids ascending from deep regions to intrude the southeast-dipping fault zone (e.g., Amezawa et al., 2023; Yoshida et al., 2023a). High He3/He4ratios were observed in hot spring waters near the southern part, indicating the presence of fluid components of deep origin (Kagoshima, et al., 2024).
The M6.5 earthquake on May 5, 2023, occurred at the shallow end of the previously identified source fault in the eastern area, with seismicity significantly extending towards the shallow extension after this earthquake. Precise hypocenter determination revealed discrepancies between the source fault of the M6.5 earthquake and the submarine active faults (Yoshida et al., 2023b; Kato, 2024).
The transient deformation, coinciding with the swarm, is predominantly attributed to slow slip events involving opening and/or reverse faulting on low–angle southeast–dipping faults located in the deeper extension zone of the swarm source areas in the western, northern, and eastern regions (Nishimura et al., 2023). This aseismic fault movement induces stress accumulation on faults within the seismic zone. The increase in stress and the intrusion of fluids into the faults of the seismic zone, prolonging swarm activity (Nishimura et al., 2023).
The hypocenter of the M7.6 event was situated between the aseismic fault and the swarm faults, suggesting that fluid intrusion into faults and stress elevation due to aseismic fault movement may have triggered fault slip around the hypocentral area.
Based on precise hypocenter determination of aftershocks and other data, it is likely that the M7.6 event was caused by the movement of offshore active faults. Aseismic fault movement induces stress buildup on the neighboring Suzu-oki and Wajima-oki segments, potentially facilitating fault rupture on both sides of the hypocenter. Furthermore, stress carried over from the 2007 M6.9 earthquake might have contributed to the westward propagation of fault rupture, ultimately culminating in the M7.6 earthquake.
Various fault models have been proposed for the M7.6 earthquake. Large slip areas were estimated on the shallow parts of the fault planes in the southwest portion of the source region and near the hypocenter, as well as in the northeastern portion of the source region, with the former two resulting in significant coastal uplift and the latter being a major contributor to the tsunami.