Updip Fluid Flow in the Crust of the Northeastern Noto Peninsula, Japan, Triggered the 2023 M_w 6.2 Suzu Earthquake During Swarm Activity

Abstract

An Mw 6.2 earthquake occurred in Suzu, northeastern Noto Peninsula, Japan, on 5 May 2023, followed by many aftershocks. Before this mainshock‐aftershock sequence, an intense earthquake swarm lasted in the vicinity for 2.5 years. Here, we estimated the rupture process of the Mw 6.2 mainshock and relocated >20,000 surrounding small earthquakes. The results show that systematic upward migration occurred via a complex network of faults in the preceding swarm period and that the mainshock rupture was initiated near the shallow end of the swarm earthquakes. The mainshock rupture propagated farther updip, followed by many aftershocks in the shallow extension. Upward fluid movement likely caused systematic upward earthquake migration from a depth of 18–5 km. The present results indicate the importance of monitoring swarm events since large (M > 6) and dangerous earthquakes can occur during such swarms.

Coseismic and Early Postseismic Deformation of the 2024 Mw7.45 Noto Peninsula Earthquake

“…Studies have revealed that fluid movement seems to play a significant role in natural earthquake swarms that occur in the overriding plates of subduction zones (Bianco et al, 2004;Iio et al, 2002;Okada et al, 2015;Yoshida et al, 2016;Yukutake et al, 2011). Recent research (Kato, 2024;Nakajima, 2022;Nishimura et al, 2023;Yoshida et al, 2023) has also suggested that the upward fluid flow in the crust could drive large earthquakes and long-lasting earthquake swarms in the northeastern tip of the Noto Peninsula. Ishikawa and Bai (2024) have further demonstrated that deep fluid flow triggered the 2024 earthquake.…”

Untangling the environmental and tectonic drivers of the Noto earthquake swarm in Japan

“…Regional GNSS (Global Navigation Satellite System) positioning suggests a volumetric increase of ∼1.4 × 10 7 m 3 in the first 3 months of the swarm, suggesting that fluid migration may be the cause of the Noto earthquake swarms ( 2 ). Amezawa et al ( 3 ) assert that crustal earthquake swarms exhibit distinct spatiotemporal patterns of earthquake migration, characterized by clusters that originate at depth and migrate upward, suggesting the presence of fluids as the driving factor behind such swarms; in the case of Noto, the source of such crustal fluids is likely from a concealed magma system ( 4 ) or slab-derived fluids ( 5 ). A three-dimensional (3D) analysis of seismic velocity structure ( 6 ) reveals a low-velocity zone beneath the Noto Peninsula, indicative of a localized zone of high pore pressure caused by fluids dehydrated from the subducted Pacific plate to the source region of the overlying crustal earthquake swarm.…”

A Multiplex Rupture Sequence Under Complex Fault Network Due To Preceding Earthquake Swarms During the 2024 Mw 7.5 Noto Peninsula, Japan, Earthquake

“…It is not rare to have modest to large magnitude (M) 6 class earthquakes in this region; recent major events include the 2007 M 6.9 and the 2023 M 6.5 earthquakes (Hiramatsu et al, 2008;Japan Meteorological Agency, 2024;Yoshida, Uno, et al, 2023) (Figure 1). The 2023 M 6.5 event, which occurred in the northern tip of the peninsula, was preceded by the long lived earthquake swarms from early November 2020 (Amezawa et al, 2023;Kato, 2024;Shelly, 2024;Yoshida, Uchida, et al, 2023;Yoshida, Uno, et al, 2023). Geodetic analyses suggest a series of transient aseismic to seismic deformation from deep to shallow domains, that is aseismic deformation caused by fluid spreading from depth, which triggered up-dip earthquake swarm activity (Nishimura et al, 2023).…”