Kinematic source rupture on listric faults for the 2024 Noto Peninsula, Japan, earthquake (Mw 7.5) estimated from near-field strong-motion waveforms

On January 1, 2024, an Mw 7.5 reverse-fault earthquake occurred along the submarine active faults just offshore of the Noto Peninsula in central Japan. This earthquake is one of the largest inland crustal earthquakes that ever recorded in Japan. We performed inversions of near-field strong-motion waveforms (0.05-0.25 Hz) to investigate the kinematic rupture process of this earthquake. For the inversions, we assumed listric fault planes, where the dip angles are steeper near the seafloor and become gentler with increased depth, based on the location of the submarine fault offsets, the structure at shallow depths revealed by seismic reflection surveys, and the relocated aftershock distribution at deep depths. To constrain our kinematic source model, we also utilized geodetic information published by the Geospatial Information Authority of Japan. We identified that the rupture process had three phases. The first phase was the initial rupture with a small slip of similar to 2 m around the rupture initiation area. After several seconds, the second and third phases, which were the main ruptures, propagated in the southwest and northeast directions, respectively. During the second and third phases, five large slip areas with average slips of 5-6 m significantly contributed to the strong-motion waveforms. By forward-simulating the geodetic data, we found that the rupture at shallow depths included an oblique component close to a right-lateral component and that, in the eastern part of the source region, the rupture transferred from a southeastward-dipping fault to a northwestward-dipping fault. The listric fault with high dip angles at shallow depths is better than a planar fault with a single dip angle for accurately modeling the fault slip near the surface and the coseismic displacement close to the fault trace during the reverse-fault earthquake.