10:45 〜 11:00
[SCG46-16] Implications of fault-valve behavior illuminated by early aftershock evolutions
★Invited Papers
Following the Mj6.5 (Mw6.2) event that occurred on 5 May 2023 near the northern shoreline of the northeastern tip of the Noto Peninsula, central Japan, rapid expansion of early aftershocks can be identified by applying the matched filter technique to continuous waveform data (Kato 2024, doi.org/10.1029/2023GL106444). Similar rapid expansion of early aftershocks can be identified following the largest aftershock Mj5.9 on the same day. These observations may be the first seismic evidence of the rapid migration of early aftershocks. The upward migration of the aftershock zone supports fault-valve behavior. The fault-valve model is defined by the cyclic nature of fluid pressures within the fault zone, whereby they gradually increase during inter-seismic periods owing to sealing/healing at the base of the brittle fault zone, resulting in overpressured fluids beneath the seismogenic zone. The increased permeability due to the coseismic generation of fractures in the fault damage zone leads to postseismic fluid discharge along the fault from the overpressured portions of the crust. The strong involvement of crustal fluids in the Noto Peninsula earthquake swarm suggests that upward migration of the initial aftershocks could be driven by the rapid upwelling of crustal fluids along the fractured permeable fault zone.