New Satellite’s Observations Close Blind Spot in Tsunami Science

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• Alex Fox- [email protected]

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When a magnitude 8.8 earthquake struck off Russia's Kamchatka Peninsula on July 29, 2025, it generated a tsunami that raced across the Pacific, with waves reaching more than 17 meters (55 feet) above sea level in the Russian coastal town of Severo-Kurilsk.

Now, an international research team has used the Surface Water and Ocean Topography(SWOT) satellite to capture wave patterns near the earthquake's source. Detecting those patterns allowed the team, which was led by San Diego State University (SDSU) and also included four researchers from UC San Diego's Scripps Institution of Oceanography, to trace the earthquake slip to within 10 kilometers (six miles) of the ocean trench along the Kamchatka subduction zone. Oceanic trenches such as this one are critical to observe because of their role in tsunami generation, but they have long been out of reach for traditional monitoring tools.

The findings, published March 26 inthe journal Science, could help scientists build more accurate models of how major earthquakes generate tsunamis and eventually inform coastal hazard preparedness.

Current tsunami monitoring relies on coastal tide gauges and a network of pressure sensors placed on the seafloor known as DART(Deep-ocean Assessment and Reporting of Tsunamis). While essential for warning systems, these instruments only provide measurements at single points that are often spaced far apart and also tend to miss shorter wavelength waves. These isolated measurements make it hard to appreciate broader patterns of waves that allow scientists to work backwards to reconstruct where and how the seafloor ruptured.

Historically, satellite measurements of tsunamis have come from instruments called altimeters, which use radar pulses to precisely measure changes in sea surface height directly beneath the satellite. Conventional satellite altimeters have occasionally captured tsunamis from orbit when their paths happen to cross, but these satellites only collect measurements along a single narrow track, which also makes any broader wave pattern difficult to detect.

That leaves a blind spot in a key area. In subduction zones, where one tectonic plate dives beneath another, the trench is the cleft on the seafloor where the plates meet. Such trenches are among the deepest parts of the ocean but are the part of the fault closest to Earth's surface. Earthquake slip in this zone can be particularly consequential for tsunami generation, but it is also the hardest to observe.

"Subduction zones host some of the largest and most devastating earthquakes on Earth," said Yao Yu, a postdoctoral researcher at Scripps and co-author of the study. "When the seafloor suddenly shifts at these undersea trenches, it pushes the ocean water above, generating powerful long waves."

The U.S.-French SWOT satellite, launched in 2022, provides a broader view of the ocean with a new type of altimeter capable of measuring sea-surface height across swaths up to 120 kilometers (75 miles) wide with centimeter-level precision. About 70 minutes after the Kamchatka earthquake, SWOT was able to image the resulting tsunami, capturing not only the leading wave but also a sequence of trailing short-wavelength waves known as dispersive waves.

"SWOT transforms our satellite observations of tsunamis from one-dimensional slices and points to a snapshot of sea-surface height across a broad area similar to topographical map," said Alice Gabriel, Scripps seismologist and co-author of the study. "Being able to see the patterns of bumps and dips in the sea's topography allows us to figure out what happened at the trench, something no other observing system has been able to deliver."

When earthquake slip occurs deep on a fault, it produces long-wavelength ocean waves that all travel at roughly the same speed. But when slip extends to the part of the fault near the trench, which is actually closer to Earth's surface, it generates shorter-wavelength waves that travel more slowly, falling behind the leading tsunami and spreading out into a trailing wave train. Those short-wavelength dispersive waves are what SWOT captured.

The researchers found the pattern of those trailing waves acted like a fingerprint of earthquake slip near the trench, which allowed the team to determine whether the earthquake's rupture extended to the trench, the shallowest part of the fault, which is vital for creating accurate models of the tsunami the seismic activity produced.

To test this connection, the team built a model of the earthquake by jointly analyzing the SWOT imagery, satellite radar measurements of land deformation and measurements from five deep-ocean DART sensors. Simulations confirmed that the only way to reproduce what SWOT observed was to factor in both dispersive wave physics and near-trench slip.

The findings also place the Kamchatka observations in a broader pattern. SWOT previously observed dispersive tsunami waves near the Loyalty Islands in the South Pacific on May 19, 2023, and again following the May 2, 2025, magnitude 7.4 Drake Passage earthquake. Together, these detections suggest that dispersive tsunami waves may be more common than previously recognized, and that their scarcity in past records likely reflects observational limitations rather than rarity in nature.

The study highlights the value of the SWOT satellite's wide-swath altimetry and suggests that factoring in dispersive waves is essential for characterizing tsunamis near their source. By capturing those detailed wave patterns near the source, scientists can better understand how an earthquake ruptured and refine the models used to assess tsunami hazards. Better observations lead to better modeling, and over time, the researchers say, stronger models can support more informed planning and preparedness for communities exposed to tsunami risk.

"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 Gabriel. "That should help us build more physically realistic models of tsunami generation and improve hazard assessments for vulnerable coastlines around the world."

Ignacio Sepúlveda of San Diego State University led the study. In addition to Gabriel, Yao Yu, Matthew Brandin and David Sandwell of Scripps Oceanography co-authored the study, as well as Bjarke Nilsson of Technical University of Denmark and Matías Carvajal from Pontificia Universidad Católica de Valparaíso. The Scripps researchers were supported by NASA, the Office of Naval Research, the University of New Hampshire and Schmidt Sciences.