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The Evolution Process Between the Earthquake Swarm Beneath the Noto Peninsula, Central Japan and the 2024 M 7.5 Noto Hanto Earthquake

Description: 

Understanding the nucleation process of large earthquakes is crucial for forecasting damaging earthquakes and seismic hazard mitigation. While the nucleation process has been identified in the laboratory settings and numerical simulations, it is difficult to observe them directly in the field. Foreshocks may be considered as a by-product of such nucleation process. While many large earthquakes have foreshocks, it is challenging to effectively distinguish foreshocks from background earthquake sequences. Several physical mechanisms of foreshocks, such as pre-slip, cascade triggering, migratory aseismic slip, and fluid-driven models, have been proposed. However, it is still not clear which model(s) play the most important role in driving the foreshocks and mainshock nucleation for a specific sequence. In this study, we focus on the relationship between an intensive earthquake swarm that started beneath the Noto Peninsula in Central Japan since November 2020 and the nucleation of the 2024 M7.5 Noto Hanto earthquake. We perform back-projection of high-frequency teleseismic P waves of the M7.5 mainshock to better understand the rupture initiation and propagation. In addition, we relocate earthquakes listed in the standard Japan Meteorological Agency (JMA) catalog with the double-different relocation method, and compute Coulomb stress changes from the M 5.5 and 4.6 foreshocks that occurred about 4 and 2 minutes before the M7.5 mainshock. Our back-projection results show a prolonged initial rupture process near the mainshock hypocenter lasting for ~25 sec, before propagating bi-laterally outward. In addition, the Coulomb stress changes from the M5.5 foreshock were negative at the hypocenter of the M7.5 mainshock, inconsistent with the cascade triggering model. Our results suggest a complex nucleation process of the M7.5 mainshock, which cannot be simply explained by either of the aforementioned physical models. Instead, we propose that a combination of fluid migration, aseismic slip and elastic stress triggering, likely work in concert to drive both the prolonged earthquake swarm and the nucleation of the M7.5 mainshock.

Session: The 2024 Magnitude 7.5 Earthquake and the Associated Earthquake Swarm Beneath the Noto Peninsula, Central Japan - II

Type: Oral

Date: 5/3/2024

Presentation Time: 11:15 AM (local time)

Presenting Author: Zhigang

Student Presenter: No

Invited Presentation: 

Authors