Lateral extent of coseismic slip and limited shallow rupture during the 29 July 2025 Kamchatka earthquake illuminated by geodetic and tsunami data

Abstract

Modern satellite-based geodetic observations reveal the coseismic deformation of the 29 July 2025 moment magnitude 8.8 Kamchatka earthquake, providing valuable constraints on the rupture characteristics along the Kuril-Kamchatka subduction zone. Satellite radar images show that notable deformation primarily occurred in the coastal area southwest of the epicenter, with GNSS measurements recording about 1.7 meters of horizontal displacement and 0.2 meters of subsidence. The coseismic slip extended at least 480 kilometers southwestward from the mainshock, with a maximum slip of 9 meters on the plate interface. The updip and downdip limits of the rupture are constrained by tsunami and satellite observations, respectively, indicating that the main slip occurred at depths of about 13–46 km. Although our preferred model indicates limited shallow rupture, the occurrence of outer-rise aftershocks suggests localized slip near the trench, implying along-strike variations in the shallow coseismic slip distribution. Our findings suggest that the northern adjacent section of the megathrust and the updip portion of the inferred rupture zone may carry an elevated tsunami risk, highlighting the need for continued monitoring. This work also emphasizes the importance of seafloor geophysical observations in subduction zones, as inland data often provide limited resolution for megathrust faults.