On 29 July 2025, an Mw 8.8 megathrust earthquake occurred offshore of the southeastern Kamchatka Peninsula, ranking among the ten largest earthquakes worldwide since 1900. Due to observational limitations, the rupture characteristics of large earthquakes along the Kamchatka subduction zone and the north–south contrast in earthquake magnitudes remain poorly understood. In this study, we combine InSAR data, GNSS displacements, and teleseismic waveforms to investigate the spatiotemporal evolution of the 2025 mainshock by constructing a curved fault geometry with along-strike and downdip variations and applying finite-fault inversion together with back-projection analysis. The inversion results show that the mainshock was characterized by unilateral rupture propagating from northeast to southwest, with a rupture length of about 560 km, a duration of about 200 s, and dominant slip concentrated at depths of 15–30 km, with a peak slip of about 10 m. Slip was weak during the initial nucleation stage near the hypocenter, whereas the main slip patch was located within a strongly locked region in the southern segment, and the rupture accelerated rapidly after entering that region. The back-projection results indicate that high-frequency radiation mainly migrated southwestward and was concentrated along the boundaries of the large-slip region and possible structural segmentation zones. These results indicate that the rupture behavior of the 2025 mainshock was jointly controlled by curved megathrust geometry and along-strike locking heterogeneity. The north–south contrast in earthquake size along the Kamchatka subduction zone may result from the combined effects of stronger locking and smoother megathrust geometry in the south, versus more complex fault geometry and submarine tectonic features in the north. This study provides new constraints on rupture processes, seismic cycle behavior, and regional seismic hazard along the Kamchatka subduction zone, and offers important implications for understanding the mechanisms and magnitude potential of future great earthquakes in the Kamchatka region.
Sun et al. (Tue,) studied this question.