Variable slip on persistent asperities controls the seismic and tsunami hazards of Kamchatka megathrust earthquakes

Subduction zone megathrust faults commonly generate the world’s largest earthquakes and associated tsunami hazards at shallow depths, yet their rupture characteristics remain poorly constrained owing to sparse observations across hundreds to thousands of kilometers from the trench. Here, we integrate inland geodetic data (GNSS and InSAR) with offshore tsunami waveforms to jointly image the coseismic slip distribution and tsunami initial source of the 2025 Mw 8.8 Kamchatka earthquake. Our tsunami-source model reveals that tsunami generation was controlled by three distinct uplifted zones (peaking at ∼5 m), each corresponding to a high-slip asperity (or coupling) on the megathrust. Our slip model shows these asperities slipped more than 6 m, with almost no slip in the deep downdip region and only limited slip at shallow depths. The limited shallow slip may have been largely compensated during the preceding 1952 event. Remarkably, the near-field spatial pattern of tsunami runup is broadly consistent across the 1737, 1952 and 2025 events, with comparable amplitudes for the latter two but more than 3-times higher for the former, a pattern that may reflect repeated rupture of the same along-strike asperities with variable slip amplitudes at similar depths across seismic cycles. This variability implies significant residual strain and future hazard potential, consistent with a supercycle behavior. Our findings underscore the critical role of persistent asperities in governing megathrust rupture variability and long-term tsunami hazard.