Improving tsunami hazard assessments depends on understanding what happens at the moment an earthquake ruptures beneath the seafloor, especially near deep-ocean trenches where measurements are often scarce. When a powerful magnitude 8.8 earthquake struck off Russia's Kamchatka Peninsula on July 29, 2025, it generated a tsunami that traveled across the Pacific.
New research published in Science shows spaceborne satellite altimetry can detect two-dimensional tsunami wave patterns near the earthquake's source, offering critical insight for coastal risk evaluation and preparedness planning.
The international study, led by San Diego State University Assistant Professor Ignacio Sepúlveda of the Department of Civil, Construction and Environmental Engineering in close collaboration between DTU Space at the Technical University of Denmark; Scripps Institution of Oceanography at the University of California San Diego; and the Instituto de Geografía at the Pontificia Universidad Católica de Valparaíso used data from the U.S.-French Surface Water and Ocean Topography, or SWOT, satellite. The team found that SWOT detected a distinct train of short-wavelength, "dispersive" tsunami waves within about 1,000 kilometers of the earthquake.
Researchers link those trailing tsunami waves to an earthquake rupture occurring less than 10 kilometers beneath the trench along the Kamchatka subduction zone, a critical zone under the seafloor where seismic processes are often difficult to measure with traditional land-based geodesy, seismic instruments or deep-water tsunami sensors.
"We're illuminating properties of earthquakes that advance our knowledge and may clarify scientific questions for the community," Sepúlveda said. "This helps us improve our understanding of earthquakes that rupture close to the trench and helps coastal communities better prepare for the seismic and tsunami hazards they face."
Megathrust earthquakes along subduction zones can abruptly displace the seafloor, generating long ocean waves capable of crossing entire ocean basins. Yet processes near the trench, where one tectonic plate dives beneath another, remain challenging to observe.
Five nearby Deep-ocean Assessment and Reporting of Tsunamis, or DART, sensors recorded the Kamchatka tsunami's leading front. The closest measured a crest-to-trough height of 1.32 meters. However, resolving shallow slip near the trench can be difficult using those records alone because sensors are spaced far apart and shorter-wavelength signals can diminish at depth.
About 70 minutes after the earthquake, SWOT passed roughly 600 kilometers seaward of the epicenter and imaged the tsunami wavefield in two dimensions. Using radar phase coherence, the satellite measures sea-surface height with centimeter-level precision. Its wide-swath observations captured both the leading crest and a sequence of trailing short-wavelength disturbances.
In the Kamchatka event, the trailing wave train indicates additional rupture shallower than 10 kilometers depth, with an along-strike centroid between 49.5 degrees north and 52.5 degrees north. The study shows that SWOT provides reliable constraints beyond the reach of traditional oceanographic, geodetic and seismic observations.
The research also places the Kamchatka observations in a broader pattern. SWOT previously observed dispersive tsunami waves near the Loyalty Islands on May 19, 2023, and again following the May 2, 2025, magnitude 7.4 Drake Passage earthquake. Together, these independent detections suggest that dispersive tsunami signals may be more common than previously recognized and that past gaps likely reflect observational limitations rather than rarity in nature.
"Capturing this tsunami with SWOT near its source gave us crucial data on the earthquake rupture, how it generated the resulting tsunami and the physics playing out near the trench," said Alice Gabriel, Associate Professor at Scripps Institution of Oceanography. "That should help us build more physically realistic models of tsunami generation and improve hazard assessments for vulnerable coastlines around the world."
The study highlights three key implications for hazard science: dispersive modeling is remarkably useful for characterizing tsunamis near their source; satellite altimetry can add unique constraints when it observes tsunamis close to where they begin; and wide-swath altimetry provides a transformative tool for understanding earthquake rupture and improving tsunami hazard assessments.
"These dispersive wave trains are not just a curiosity. They carry information about where the locked fault – which causes energy to build up over decades to centuries of plate motion – slipped during the earthquake. In particular, they provide unique evidence for slip very close to the trench, which is otherwise extremely difficult to constrain," said Matías Carvajal, Professor at Instituto de Geografía.
"This discovery shows the importance of the U.S. and the world investing in satellite capacity measuring what is happening on our planet regarding geo-hazards," Sepúlveda said. "This satellite helps us understand tsunami and seismic hazards through a new lens—one that's much clearer than before."
By improving how scientists resolve near-trench earthquake behavior and the tsunami signals it produces, the research supports stronger earthquake rupture models and hazard assessment methods used to evaluate coastal risk.
"We contributed by processing data from SWOT and other satellites for the analysis. This makes it possible for other researchers to improve models of how tsunamis propagate and develop. In the long term, this could strengthen tsunami warning systems in vulnerable coastal regions," said Bjarke Nilsson, PhD student at DTU Space.
The research reflects a shared international effort to strengthen scientific understanding of earthquake-driven hazards and improve the foundation for tsunami hazard assessments worldwide.
