Limited near-trench slip of the 2025 Mw 8.7-8.8 Kamchatka earthquake from geodetic and tsunami data

The Kamchatka subduction zone marks one of the most tectonically active regions in the world. Along the Kuril-Kamchatka Trench, the dense, cold Pacific plate subducts beneath the Okhotsk plate, accommodating a shortening rate of ~80 mm/yr along a direction almost perpendicular to the trench. Numerous tsunamigenic earthquakes have been documented along this subduction zone, including the 1952 M_w 8.8-9.0 megathrust earthquake that remains one of the largest events ever recorded by modern instruments. Similar megathrust events are suspected to have occurred in 1737 and 1841, although the observations from those times are scarce. On 29 July 2025, a M_w 8.7-8.8 earthquake occurred offshore Kamchatka, generating a tsunami that traveled across the Pacific. The 2025 epicenter lies less than 40 km from that of the 1952 earthquake and is accompanied by an aftershock distribution of comparable extent. The 2025 event therefore presents a rare opportunity to study the megathrust rupture on the Kamchatka plate interface using modern satellite-based geodesy.

We analyzed coseismic deformation of the 2025 Kamchatka earthquake using InSAR from multiple satellites and GNSS. InSAR images show deformation concentrated in the southern Kamchatka Peninsula, with amplitudes increasing progressively from inland areas toward the coast. The GNSS station on Paramushir Island recorded the maximum GNSS displacement, with seaward horizontal and downward vertical motions of ~1.7 m and ~0.2 m, respectively. Slip inversions suggest that the rupture propagated unilaterally from the epicenter to the southwest for ~480 km, broadly consistent with the aftershock distribution. The coseismic slip extended downdip to a depth of ~46 km, where the satellite-based geodetic data provide sufficient resolution. However, we found that inland geodetic measurements are insensitive to near-trench slip. Therefore, we generated three geodetic slip models with extreme, moderate, and zero shallow slip, and used DART tsunami observations to evaluate them. As a result, the model with zero shallow slip best reproduces the tsunami arrival times at DART stations, supporting the absence of significant near-trench rupture during the mainshock. The main rupture was confined to depths of 13-46 km, with a peak slip of ~9 m and a geodetic moment magnitude of M_w 8.7. The updip shallow portion of the 2025 rupture zone and the northern adjacent section may pose an elevated tsunami risk due to stress transfer. This work further underscores the crucial role of seafloor observations, as inland data typically offer limited insight into the shallow slip behavior of subduction interfaces.