A satellite designed to measure ocean surface height delivered a remarkable result when a powerful earthquake near Russia’s Kamchatka Peninsula unleashed a tsunami that spread across the Pacific in July, last year. Scientists report in The Seismic Record that the Surface Water Ocean Topography (SWOT) satellite recorded the first high-resolution spacebased track of a major tsunami generated by a subduction zone earthquake.
This new view revealed a far more complicated wave pattern than expected, with energy spreading and scattering across the ocean. The findings could help researchers better understand how tsunamis move and how they may impact coastlines.
Angel Ruiz-Angulo of the University of Iceland and his team combined the satellite observations with readings from DART (Deep-ocean Assessment and Reporting of Tsunamis) buoys positioned along the tsunami’s path.
Together, the data provided new insight into the magnitude 8.8 earthquake that struck on July 29 in the Kuril-Kamchatka subduction zone. It ranks as the sixth-largest earthquake recorded worldwide since 1900. “I think of SWOT data as a new pair of glasses.
“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,” Ruiz Angulo said.
SWOT, launched in December 2022 through a partnership between NASA and the French space agency Centre National d’Etudes Spatiales, was built to map Earth’s surface water on a global scale. Ruiz-Angulo noted that he and co-author Charly de Marez had spent more than two years studying SWOT data to analyze 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. Scientists have long assumed that very large tsunamis behave as “non-dispersive” waves.
Because their wavelengths are longer than the depth of the ocean, they are expected to travel largely intact as a single wave rather than breaking apart into multiple waves. “The SWOT data for this event has challenged the idea of big tsunamis being nondispersive,” Ruiz-Angulo explains.
Instead, the satellite observations showed evidence of dispersion, where the wave energy spreads into multiple components. Computer simulations that included this type of behavior 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.
“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,” RuizAngulo added.
