Long‐Living Earthquake Swarm and Intermittent Seismicity in the Northeastern Tip of the Noto Peninsula, Japan

Abstract

Earthquake swarms are patterns of seismic activity that have no clear mainshock and continue for a specific period (e.g., Mogi, 1963). Swarms are often observed around volcanoes, geothermal sites, and anthropogenic fluid injection wells (e.g., Chen & Shearer, 2011;Horton, 2012;Yukutake et al., 2011). Previous studies have revealed some of the driving factors of swarms, such as the shear strength of faults or changes in the stress state around the swarm area by highly pressurized fluid intrusion (e.g.,

Implications of Fault‐Valve Behavior From Immediate Aftershocks Following the 2023 Mj6.5 Earthquake Beneath the Noto Peninsula, Central Japan

“…Amezawa et al. (2023) implied that crustal fluid is a major factor influencing the spatiotemporal evolution of the long‐lasting Noto Peninsula seismic swarm based on diffusive hypocenter migrations. Therefore, we propose that the 2023 M j 6.5 event ruptured a steep pre‐existing reverse fault that has been lubricated by crustal fluids that have migrated upward from a deep fluid‐rich zone in the lower crust (Figure 4).…”

“…Nishimura et al (2023) used geodetic data to suggest that the upwelling fluid spread at ∼16 km depth through an existing shallow-dipping permeable fault zone and then diffused into the fault zone (Figure 4). Amezawa et al (2023) implied that crustal fluid is a major factor influencing the spatiotemporal evolution of the long-lasting Noto Peninsula seismic swarm based on diffusive hypocenter migrations. Therefore, we propose that the 2023 M j 6.5 event ruptured a steep pre-existing reverse fault that has been lubricated by crustal fluids that have migrated upward from a deep fluid-rich zone in the lower crust (Figure 4).…”

“…The focal mechanism of each major event during the swarm sequence shows thrust faulting along an approximately NE–SW‐striking fault. Most of the earthquakes have occurred at shallow crustal depths (<16 km) and have been divided into four significant clusters (Amezawa et al., 2023; Nakajima, 2022; Yoshida et al., 2023). Diffusive hypocenter migrations have been observed over the entire period in the western, northern, and northeastern clusters (Amezawa et al., 2023).…”

“…Most of the earthquakes have occurred at shallow crustal depths (<16 km) and have been divided into four significant clusters (Amezawa et al, 2023;Nakajima, 2022;Yoshida et al, 2023). Diffusive hypocenter migrations have been observed over the entire period in the western, northern, and northeastern clusters (Amezawa et al, 2023). Nishimura et al ( 2023) modeled transient deformations using Global Navigation Satellite System observation networks by combining the relocated earthquake hypocenters and tectonic settings and revealed that the transient deformations could essentially be separated into two stages: an initial three-month-long stage when a shallow-dipping tensile crack opened at ∼16 km depth, followed by an ongoing series of shear-tensile sources, which represent aseismic thrust-faulting slip and the opening of a SE-dipping fault, at 14-16 km depth.…”

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

“…fault network (Yoshida, Uno, et al, 2023). Previous studies have suggested that fluid movement at depth and the accompanying aseismic deformation are involved in this swarm (Amezawa et al, 2023;Nakajima, 2022;Nishimura et al, 2023;Yoshida, Uno, et al, 2023). The presence of a deeper low-seismic-velocity region and a distinct seismic reflector led to the inference that the upward migration of slab-derived fluids triggered this swarm (Yoshida, Uno, et al, 2023).…”