Spatiotemporal Distribution of Coseismic Slip During the 2025 Kamchatka Earthquake Inferred from Tsunami Waveform Data

Abstract

ABSTRACT On 29 July 2025 (UTC), an earthquake with a moment magnitude of approximately 8.8 occurred along the plate interface of the Kamchatka subduction zone and generated a trans-Pacific tsunami. Using tsunami waveform data recorded at offshore stations, we conducted tsunami waveform inversion based on a multiple time-window approach to investigate the spatiotemporal distribution of coseismic slips during the earthquake. The inversion results suggest temporally distributed slip evolution, with the largest slip occurring approximately 180–225 s after the earthquake occurrence. The slip distribution indicates that the dominant asperities were located primarily in the shallow-to-intermediate portions of the fault plane, whereas the largest slip was estimated to be in the deeper region at approximately 12 m. Resolution tests of our inversion analysis suggest that slips in the shallow-to-intermediate portions of the fault plane were relatively well constrained, whereas those in the deeper region were less well resolved. This reduced resolution likely reflects the lower sensitivity of far-field tsunami observations to deep fault slip, together with limitations in the azimuthal distribution of offshore stations. The total seismic moment derived from the developed source model was 1.44×1022 N·m, corresponding to a moment magnitude of 8.7. The spatiotemporal characteristics of slips in our source model were comparable with source models developed by previous studies using other observational data.