Implications of Fault-Valve Behavior From Immediate Aftershocks Following the 2023 M_j6.5 Earthquake Beneath the Noto Peninsula, Central Japan

The M(j)6.5 (M(w)6.2) event that occurred on 5 May 2023 near the northern shoreline of the northeastern tip of the Noto Peninsula, central Japan, is the largest event to date in a long-lasting, intense earthquake swarm. Here we have created a more precise aftershock catalog associated with the 2023 M(j)6.5 and the second-largest 2022 M(j)5.4 sequence to understand the rupture process of this largest earthquake. Most of the aftershocks are aligned along a similar to 45 degrees SE-dipping plane. The mainshock initially ruptured the same deep section of the fault zone that had been ruptured by the 2022 M(j)5.4 event, before propagating rapidly to shallow depths and to offshore along the ruptured fault plane. The aftershock front migrated at a speed of similar to 20 km/hr. This rapid upward migration of the immediate aftershocks might be driven by upwelling of crustal fluids along the intensely fractured and permeable fault zone via mainshock dynamic rupture.