A satellite designed to measure the height of the ocean surface was in the right place at the right time when a powerful earthquake off Russia’s Kamchatka Peninsula sent a tsunami across the Pacific in late July.
The spacecraft, known as the Surface Water Ocean Topography or SWOT satellite, recorded the first high resolution space-based track of a major subduction zone tsunami, according to researchers writing in The Seismic Record.
Instead of a simple wave moving cleanly across the ocean, the satellite data revealed a surprisingly intricate pattern of waves spreading, interacting, and scattering across the basin. Scientists say this detailed view could improve understanding of how tsunamis travel and how they may ultimately affect coastlines.
Combining satellite data with ocean sensors
To better understand the event, Angel Ruiz-Angulo of the University of Iceland and his colleagues combined the satellite observations with measurements from DART (Deep-ocean Assessment and Reporting of Tsunamis) buoys located along the tsunami’s path. These deep-ocean sensors helped them refine estimates of the earthquake that triggered the waves.
The July 29 earthquake struck in the Kuril-Kamchatka subduction zone with a magnitude of 8.8, making it the sixth largest earthquake recorded worldwide since 1900.
“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 for water, not disasters
SWOT was launched in December 2022 as a joint mission between NASA and the French space agency Centre National d’Etudes Spatiales. Its main goal is to deliver 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 studying SWOT data to understand everyday ocean features such as small eddies. “[We] 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.”
Rethinking how giant tsunamis behave
Because the wavelength of large tsunamis is much longer than the depth of the ocean, scientists have traditionally described them as “non-dispersive.” In simple terms, this means the wave is expected to travel as a single, stable form rather than breaking into multiple waves that spread out over time.
“The SWOT data for this event has challenged the idea of big tsunamis being non-dispersive,” Ruiz-Angulo explains.
When the team compared the satellite observations with computer simulations, they found that tsunami models that included dispersion matched the real-world data more closely than traditional 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.”
A longer earthquake rupture than expected
The researchers also noticed a mismatch between tsunami arrival times predicted by earlier models and the actual measurements recorded by two DART tide gauges. One gauge recorded the tsunami earlier than expected, while the other detected it later.
Using the buoy data in a technique known as inversion, the team reexamined the source of the tsunami. Their analysis suggested the earthquake rupture extended farther south than previously thought and stretched about 400 kilometers — significantly longer than the 300 kilometers estimated by other models.
“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 study co-author Diego Melgar.
Why mixing data matters
Since that 2011 disaster, Melgar’s research group and others have worked to better integrate DART buoy data into earthquake and tsunami analyses. However, this approach is still not routine.
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 on record, including a devastating event in 1952 triggered by a magnitude 9.0 earthquake. That disaster led to the creation of the international tsunami warning system that later issued alerts across the Pacific during the 2025 event.
“With some luck, maybe one day results like ours can be used to justify why these satellite observations are needed for real or near-real time forecasting,” Ruiz-Angulo said.
