Earth, Planets and Space (Apr 2025)
Source rupture process of the M W 6.2 earthquake in the Noto Peninsula, central Japan, on May 5, 2023
Abstract
Abstract An M JMA 6.5 crustal earthquake occurred during earthquake swarm activity around the northeastern tip of the Noto Peninsula, central Japan, on May 5, 2023. To elucidate the position of this earthquake in the continuing seismic swarm activity, it is necessary to clarify the relationships between the source rupture process, crustal structure, and the earthquake swarm activity. The kinematic source rupture process of this event was analyzed using strong-motion waveform records observed at strong-motion stations surrounding the source region using the finite source inversion method, incorporating a three-dimensional velocity model in the target area. The rupture propagated mainly in the up-dip direction on a source fault plane dipping southeastward at an angle of 40°. A significant slip with a maximum slip amount of 0.8 m was found in the depth range of 8–11 km, which is approximately 4 km in the up-dip direction from the hypocenter. The slip direction was thrust type, with a small right-lateral strike-slip component. The location of this asperity corresponded to the region of low V P/V S ratio. The total seismic moment was 2.40 × 1018 Nm (M W 6.2). Most slips occurred at depths shallower than those of the preceding seismic activity, which occurred primarily at depths from 10 to 14 km. The seismic activity immediately after this earthquake occurred around the large-slip area, with intensive earthquakes occurring at shallow depths (< 10 km). Active seismic activity in and around the rupture area of the M W 6.2 earthquake on May 5, 2023, continued intensively even after this earthquake, and then the rupture of the 2024 Noto Hanto earthquake (M JMA 7.6) on January 1, 2024, started at the southwestern edge of the asperity of the M W 6.2 earthquake. Therefore, this earthquake can be interpreted as one of turning point in this earthquake swarm activity to connect the preceding swarm in the depth range from 10 to 15 km with seismic activity in shallower depths including the further destructive event. Graphical Abstract
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