SWOT Satellite Altimetry Observations and Source Model for the Tsunami from the 2025 <b>M</b>  8.8 Kamchatka Earthquake

Abstract On 29 July 2025, an Mw 8.8 earthquake struck off Kamchatka, Russia, generating a Pacific-wide tsunami and marking the largest earthquake since the launch of the surface water and ocean topography (SWOT) satellite in 2022. We analyze tsunami observations from SWOT together with three nearby deep-ocean assessment and reporting of tsunamis (DART) buoys to resolve the source of the event. SWOT provided the first high-resolution spaceborne track of a great subduction-zone tsunami, capturing waveforms that reveal complex propagation, dispersion, and scattering. Inversion of the DART time series using Gaussian unit sources shows that the rupture extended ∼400 km along strike, with peak uplift of ∼4 m, significantly different from the published finite-fault model. A blended source that combines the DART-inverted uplift with subsidence from the seismic–geodetic model best matches both datasets and reproduces the SWOT observations. Comparison with reconstructions of the 1952 Mw 9.0 Kamchatka earthquake indicates that the 2025 rupture likely reactivated significant portions of the megathrust that broke in 1952 but occurred farther down-dip and with little to no near-trench slip, consistent with its smaller tsunami impact. These findings highlight the hazard implications of short recurrence intervals of great earthquakes and show how rupture style governs tsunami severity. They also demonstrate the value of satellite altimetry for improving tsunami source characterization, post-event forecasting, and understanding of hydrodynamic processes.