Space-based observations shed new light on tsunami dynamics

A NASA satellite built to study the movement of Earth’s surface water has unexpectedly provided scientists with one of the most detailed views yet of how a giant tsunami behaves as it travels across the open ocean, and what it revealed challenged long-held assumptions.

In July 2026, a powerful earthquake off Russia’s Kamchatka Peninsula sent a tsunami rippling across the Pacific Ocean. By chance, the Surface Water Ocean Topography (SWOT) satellite was positioned directly over the disturbance, allowing it to capture the first high-resolution, space-based track of a major tsunami generated by a subduction-zone earthquake. Researchers later described the findings in The Seismic Record.

What the satellite observed was not the single, smooth wave scientists often expect to see. Instead, the data showed a complex pattern of waves spreading outward, interacting with one another, and scattering across the ocean basin. According to researchers, this unexpected level of detail could reshape how tsunamis are understood, modelled, and eventually forecast as they approach coastlines.

To analyse the event more closely, Angel Ruiz-Angulo of the University of Iceland and his colleagues combined the SWOT observations with readings from DART (Deep-ocean Assessment and Reporting of Tsunamis) buoys positioned along the tsunami’s path. These deep-ocean instruments helped the team refine estimates of the earthquake that triggered the waves.

The quake struck the Kuril-Kamchatka subduction zone on July 29 with a magnitude of 8.8 on the Richter scale, ranking it as the sixth-most powerful earthquake recorded worldwide since 1900.

“I think of SWOT data as a new pair of glasses,” Ruiz-Angulo said. “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 kilometres wide, with unprecedented high-resolution data of the sea surface,” he added.

SWOT was never designed to track disasters. Launched in December 2022 as a joint mission between NASA and France’s Centre National d’Etudes Spatiales, its primary goal is to create the first global survey of Earth’s surface water, including oceans, rivers, and lakes.

Ruiz-Angulo said he and co-author Charly de Marez had spent more than two years examining SWOT data to understand routine ocean features such as small eddies. “We had been analysing 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,” he said.

Beyond the rare observation itself, the data raised deeper scientific questions. Large tsunamis are traditionally classified as “non-dispersive,” meaning they are expected to travel as a single, stable wave because their wavelengths are far longer than the depth of the ocean.

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

When researchers compared the satellite measurements with computer simulations, they found that models accounting for wave dispersion aligned more closely with what was actually observed than conventional approaches.

“The main impact that this observation has for tsunami modellers is that we are missing something in the models we used to run,” Ruiz-Angulo said. He suggested the extra variability could mean the main wave is influenced by trailing waves as it nears the coast, an effect that has not been fully considered before.

The team also noticed inconsistencies between predicted tsunami arrival times and what two DART tide gauges recorded. One gauge detected the tsunami earlier than expected, while the other recorded it later. By reanalysing the data through a technique known as inversion, the researchers concluded that the earthquake rupture may have extended farther south than previously believed, stretching roughly 400 kilometres rather than the earlier estimate of 300 kilometres.

“Ever since the 2011 magnitude 9.0 Tohoku-oki earthquake in Japan, we realised that the tsunami data had really valuable information for constraining shallow slip,” said study co-author Diego Melgar.

The findings underscore the importance of combining multiple data sources. While incorporating DART data into earthquake analysis has improved since 2011, Melgar noted it is still not routine because ocean and seismic models are often treated separately.

The Kuril-Kamchatka region has generated some of the world’s largest tsunamis, including a devastating event in 1952 that ultimately led to the creation of the international tsunami warning system.

“With some luck,” Ruiz-Angulo said, “maybe one day results like ours can be used to justify why these satellite observations are needed for real or near-real-time forecasting.”