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The 2024 Mw 7.5 Noto Peninsula Earthquake Initiated in a Fluid-Driven Swarm

Description: 

On 1 January 2024, an Mw 7.5 earthquake rupture occurred along the northern coast of the Noto Peninsula, Ishikawa Prefecture, and its eastern extension. The northeastern tip of the Peninsula, near the Mw7.5 hypocenter, has seen a rapid increase in seismicity since the end of 2020, attracting much attention. This talk will present the characteristics and implications of the spatio-temporal distribution of earthquakes before and after the Mw 7.5 earthquake, revealed from regional seismic data.

During the earthquake swarm before the mainshock, small earthquakes systematically moved to the shallow side via a complex fault network (Yoshida et al., 2023, JGR). Seismicity was initiated in a locally deep cluster, with a distinct S-wave reflector and seismic low-velocity zone below. Unusual crustal deformations, the magnitude of which was much larger than that of the swarm earthquakes, were observed around the hypocenter (Nishimura et al., 2023). The 2023 Mw 6.2 earthquake occurred near the upper end of one of a fault zone, propagating in the updip direction, with aftershocks occurring further shallow on the same fault (Yoshida et al., 2023, GRL). The Mw7.5 mainshock started near the fault zones of the swarm and eventually ruptured both the east and west sides. Aftershocks occur within a range of 150 km but are basically concentrated on the north-northeast dipping plane to the west and the south-southeast dipping plane to the east.

Upward migration of fluids likely triggered the swarm activity and aseismic deformations before the mainshock. The present observation indicates that Mw7.5 earthquakes can be initiated by fluid-driven swarm activity. Presumably, considerable strain energies may have accumulated in the main rupture regions before the mainshock, where the properties (e.g., temperature and heterogeneity) may differ from those in the swarm region. In the source region of the prior swarm earthquakes, earthquakes started to occur at a shallower plane than before, and this plane may coincide with a known active fault. Upward migration of fluids may still be ongoing there.

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: 11:00 AM (local time)

Presenting Author: Keisuke

Student Presenter: No

Invited Presentation: Yes

Authors