The satellite, called Surface Water Ocean Topography (SWOT), recorded the first high resolution, wide area view of a major tsunami generated by a subduction zone earthquake, according to research published in The Seismic Record.

What scientists found was unexpected. Rather than moving across the ocean as a relatively simple wave, the tsunami displayed a far more complicated pattern, with waves spreading, scattering, and interacting across vast stretches of the Pacific. The discovery could help researchers improve tsunami forecasting and better understand potential risks to coastal communities.

A Rare View of a Pacific-Wide Tsunami

The tsunami was triggered by a magnitude 8.8 earthquake on July 29 in the Kuril-Kamchatka subduction zone, where one tectonic plate is forced beneath another. The quake ranks as the sixth largest earthquake recorded anywhere in the world since 1900.

To study the event, researchers combined observations from the SWOT satellite with measurements from DART (Deep-ocean Assessment and Reporting of Tsunamis) buoys positioned throughout the Pacific. These instruments are designed to detect subtle changes in sea level and provide early warning information during tsunami events.

According to lead author Angel Ruiz-Angulo of the University of Iceland, the satellite provided a dramatically different perspective than scientists have had in the past.

"I think of SWOT data as a new pair of glasses," said Ruiz-Angulo. "Before, with DARTs we could only see the tsunami at specific points in the vastness of the ocean. There have been other satellites before, but they only see a thin line across a tsunami in the best-case scenario. Now, with SWOT, we can capture a swath up to about 120 kilometers wide, with unprecedented high-resolution data of the sea surface."

A Satellite Built to Study Water

SWOT was launched in December 2022 as a joint mission between NASA and the French space agency Centre National d'Etudes Spatiales. Its primary goal is to create the first comprehensive global survey of Earth's surface water, tracking everything from rivers and lakes to ocean features.

Ruiz-Angulo said he and co-author Charly de Marez had spent more than two years analyzing SWOT observations of ocean processes such as small eddies and currents before this rare opportunity appeared.

They "had been analyzing SWOT data for over two years understanding different processes in the ocean like small eddies, never imagining that we would be fortunate enough to capture a tsunami."

Challenging a Long-Held Assumption About Tsunamis

One of the study's most surprising findings involves a concept known as dispersion.

Scientists have traditionally viewed large tsunamis as "non-dispersive." Because their wavelengths are much longer than the depth of the ocean, researchers generally expect these waves to maintain a relatively consistent shape as they travel long distances.

In a dispersive wave system, however, different parts of the wave move at slightly different speeds. This can cause the original wave to spread out into a leading wave followed by a series of trailing waves.

"The SWOT data for this event has challenged the idea of big tsunamis being non-dispersive," Ruiz-Angulo explains.

When the team compared the observations with computer simulations, they found that models including dispersion matched the satellite measurements more closely than traditional tsunami models.

"The main impact that this observation has for tsunami modelers is that we are missing something in the models we used to run," Ruiz-Angulo added. "This 'extra' variability could represent that the main wave could be modulated by the trailing waves as it approaches some coast. We would need to quantify this excess of dispersive energy and evaluate if it has an impact that was not considered before."

Tsunami Data Reveals a Larger Earthquake Rupture

The tsunami observations also helped researchers refine their understanding of the earthquake itself.

Earlier models based on seismic measurements and land deformation predicted tsunami arrival times that did not fully match what was recorded by two DART gauges. One station detected the tsunami earlier than expected, while another recorded it later than predicted.

To investigate the discrepancy, the team used a technique called inversion, which works backward from observed tsunami behavior to estimate the characteristics of the earthquake that generated it.

Their analysis suggested the earthquake rupture extended farther south than previous studies indicated. The rupture stretched roughly 400 kilometers, significantly longer than the 300 kilometers estimated by earlier models.

Study co-author Diego Melgar noted that tsunami observations have become increasingly valuable for understanding how large earthquakes rupture near the seafloor.

"Ever since the 2011 magnitude 9.0 Tohoku-oki earthquake in Japan, we realized that the tsunami data had really valuable information for constraining shallow slip," said Melgar.

Why Multiple Data Sources Matter

Following the devastating 2011 Japan earthquake and tsunami, researchers began placing greater emphasis on combining different types of observations when studying major earthquakes.

Melgar explained that incorporating DART buoy measurements into earthquake analyses remains challenging because the physics used to model ocean waves differs from the physics used to model seismic waves traveling through Earth's crust.

Since then, Melgar's lab and others have been working on ways to include DART data in inversions, "but it is still not always done because the hydrodynamic models needed to model DARTs are very different than the seismic wave propagation ones for modeling the solid Earth data. But, as shown here again, it is really important we mix as many types of data as possible," Melgar said.

Improving Future Tsunami Warnings

The Kuril-Kamchatka subduction zone has produced some of the largest tsunamis ever recorded in the Pacific. A magnitude 9.0 earthquake in the same region triggered a massive tsunami in 1952, an event that ultimately helped drive the creation of the international tsunami warning system.

That warning network later played a key role in issuing Pacific-wide alerts during the 2025 tsunami.

As satellite technology continues to improve, researchers hope observations like those collected by SWOT could one day become part of near real time tsunami forecasting systems, helping provide faster and more accurate warnings for communities in harm's way.