Researchers combining two methods to reconstruct the rupture evolution of the July 2025 magnitude 8.8. Kamchatka earthquake found the rupture from the megathrust event extended about 500 kilometers from its epicenter.
The rupture extent closely overlaps the rupture of the magnitude 9.0 1952 Kamchatka earthquake, according to the report by Guilherme de Melo of GEOMAR Helmholtz Centre for Ocean Research and his colleagues in The Seismic Record.
This unusual similarity suggests ruptures in the region may be controlled by some structural feature of the megathrust margin, the researchers conclude.
de Melo and colleagues used two methods, teleseismic back-projection and hydroacoustic T-waves, to investigate the 2025 Kamchatka rupture length, duration, velocity and propagation direction.
Teleseismic back-projection produces an image of earthquake rupture by collapsing high-frequency seismic wavefronts backward in space and time, using data collected by seismic stations that can be 1000 to 10,000 kilometers away from the earthquake's source.
Hydroacoustic T waves are generated along the seafloor when the strong underwater seismic energy generated by earthquakes couples into the oceanic water layer and propagates for thousands of kilometers with low attenuation within the Sound Fixing and Ranging or SOFAR channel, a layer of the ocean that acts like a natural acoustic waveguide.
The Kamchatka earthquake offered a great opportunity to combine the two methods because the event produced both strong teleseismic signals and intense hydroacoustic T waves, de Melo noted. The earthquake was recorded both by seismic networks and the H11N hydrophone array in the Pacific Ocean, which is deployed as part of the International Monitoring System for nuclear test monitoring.
"We were interested not only in characterizing the earthquake rupture itself, but also in testing whether hydroacoustic observations could provide rupture features consistent with those obtained from the teleseismic back-projection approach," de Melo explained. "The good agreement between the two approaches was one of the most interesting outcomes of the study."
The two methods both revealed a predominantly southwestward rupture that extended about 500 kilometers from the earthquake epicenter. The rupture length is about 60-70 kilometers longer than might be expected for a magnitude 8.8 earthquake, the researchers calculated.
The study also notes that other recent megathrust earthquakes have produced rupture lengths that exceed those calculated using common magnitude-rupture scaling relationships. One example is the 2004 magnitude 9.0 Sumatra-Andaman earthquake, which had a rupture about 2.5 times longer than expected by its magnitude.
de Melo noted that the team's findings add to a growing body of evidence that other factors influence rupture length.
"Factors such as the fault geometry, the distribution of stress on the fault, asperities along the slab structure, and variations of the seafloor material properties along the ruptured area may affect the rupture velocity and extend the rupture propagation," he said.
In an earlier study , for instance, de Melo and colleagues show how hydrated and less rigid crust along certain ocean faults can lead to longer ruptures from strike-slip earthquake events.
"What makes the Kamchatka case particularly interesting is that the 2025 rupture appears to overlap, within uncertainties, the area affected by the great 1952 Kamchatka earthquake," de Melo said. "This suggests that local structural features of the Kamchatka boundary may influence the extension of very large ruptures over many decades."
Large subduction zones contain variations in sediment thickness, seafloor topography, plate geometry and other features that can potentially affect rupture length. "However, the exact nature of those controls [for the Kamchatka megathrust] remains uncertain and will require further studies," said de Melo.
