Assessing Pre-Seismic Deformation in Southern Kamchatka: A Joint SBAS-InSAR and GNSS Analysis Prior to the July 29, 2025 Earthquake

In the subduction zone of the Kamchatka Peninsula, where the powerful earthquake (Mw 8.2–8.8) of July 29, 2025, repeated the hypocenter location of the 1952 event, the task of studying the spatial heterogeneity of interseismic deformation as an indicator of the preparation for major seismic events is relevant. The aim of this work was to identify large geodynamic blocks with similar deformation parameters in the southern part of Kamchatka based on data analysis for the period preceding the specified seismic activity. A methodology that combines radar interferometry (the SBAS method implemented in the MintPy package) and Global Navigation Satellite System (GNSS) data was applied and adapted for this purpose. The technique was specifically developed for the conditions of Kamchatka – Russia's snowiest region with high atmospheric turbulence. It includes using data exclusively from the snow-free period (May–October) with a coherence threshold of 0.75; integrating GNSS measurements to fill gaps in the SBAS time series and build continuous velocity fields; and correcting for atmospheric delays. As a result of processing Sentinel-1 data for 2017–2025 and clustering the velocity fields by two components (vertical and west–east direction), a clear division of the territory into two large blocks – western and eastern – separated by a buffer zone, was revealed. It was established that the displacement rate of the eastern block (19.3–21.0 mm/yr) is several times higher than that of the western block (4.6–8.7 mm/yr). The obtained results demonstrate the effectiveness of the proposed synergistic approach for mapping the block structure and quantifying interseismic deformations in complex natural conditions, which is important for assessing seismic hazard in subduction zones.