Analysis of the Coseismic Slip Behavior for the Mw = 8.8 2025 Kamchatka Peninsula (Russia) Earthquake From Satellite Goce Vertical Gravity Gradient

The southern Kamchatka Peninsula lies along the southeastern margin of the Okhotsk microplate; a region identified with high seismic potential. This segment of the megathrust hosted the historic Great Kamchatka earthquake (Mw = 9.0) in 1952, one of the four largest ever instrumentally recorded. On July 29, 2025, an Mw = 8.8 earthquake ruptured a similar portion of the megathrust through shallow reverse faulting, which is characteristic of subduction zones. In this study, we investigate the coseismic slip behavior of this event along the Kuril-Kamchatka subduction zone by directly modeling gravity data from the GOCE satellite mission. Finite-fault models from different data sources indicate that the rupture propagated entirely southwestward. Most of these models showed that deformation was distributed across distinct patches, with the highest slip occurring to the southwest of the epicenter, mainly between 50° and 51° N, coinciding with a low anomaly of the vertical gravity gradient (Tzz). Spectral coherency between a coseismic slip distribution model and Tzz showed a correlation of about 90%. A saddle-point in the Tzz variation at 53° N marks an important seismic barrier that also constrained previous great megathrust earthquakes. The northeastern termination of foreshock and aftershock activity further supports this. Another seismic barrier was inferred at 51° N by comparing Tzz to coseismic slip and to kinematic rupture models. Our results show that the Tzz effectively maps major asperities and barriers, in agreement to the degree of interseimic coupling, as found in previous studies of other great megathrust events around the world. We conclude that the density distribution mapped from satellite GOCE indicates a primary factor controlling seismic segmentation. We also propose the Tzz as a first-order proxy for seismic hazard assessment, as well as for constraining locking and finite-fault models that require a priori information on megathrust structure.