A powerful earthquake with a magnitude of 8.8 that occurred near the Kamchatka Peninsula in Russia set off a tsunami across the Pacific in late July. A satellite specially designed to measure the height of the ocean surface completely "tracked" this huge wave from space with high resolution for the first time.
A recent study published in "The Seismic Record" pointed out that the "Surface Water and Ocean Topography" (SWOT) satellite jointly developed by the United States and France recorded the first high-resolution space observation track of a large tsunami triggered by this subduction zone earthquake. It showed a much more complex wave structure than expected, and the energy continued to spread and scatter on the vast ocean surface. Researchers believe that this result is expected to help humans gain a deeper understanding of the tsunami propagation mechanism, thereby improving the assessment of potential impacts on coastal areas.
The study was completed by University of Iceland researcher Angel Ruiz-Angulo and others. They jointly analyzed sea surface height data obtained by the SWOT satellite and DART (Deep Sea Tsunami Assessment and Reporting) buoy observation records deployed along the tsunami propagation path. The results not only revealed the unusually complex details of the tsunami waveform, but also provided new constraints for reconstructing the rupture process of this magnitude 8.8 earthquake in the Kamchatka-Kurile Arc subduction zone. This earthquake occurred on July 29 and was the sixth largest earthquake recorded in the world since 1900.
Ruiz-Angulo described SWOT data as giving researchers a “new pair of glasses.” Previously, the scientific research community mainly relied on DART buoys spread across the Pacific to obtain tsunami information, which could only "sample" and record tsunami signals at limited points on the vast ocean area. Although other satellites can also observe sea surface height changes, under ideal circumstances they can only "sweep" a thin line of the tsunami. In contrast, SWOT can acquire sea surface swath data up to about 120 kilometers wide per transit and characterize sea surface height fluctuations with unprecedented high spatial resolution.
The SWOT satellite will be launched in December 2022 and is jointly developed by NASA and the French National Center for Space Research (CNES). Its core mission is to carry out the first high-precision mapping of global surface water bodies and ocean surfaces. Ruiz-Angulo said that he and co-author Charly de Marez had previously used SWOT data to study small-scale eddies and other structures in the ocean for more than two years, and did not originally expect to have the opportunity to "bump into" a large tsunami.
This observation also forced the scientific research community to rethink the propagation characteristics of large tsunamis. For a long time, the mainstream view has been that giant tsunamis with wavelengths much larger than the average ocean depth are "non-dispersive waves" and should be dominated by overall waveforms during cross-ocean propagation, and the energy is not easily split into multiple groups of waves. However, the data of this event obtained by SWOT clearly showed the existence of the dispersion effect: the tsunami energy was decomposed into multiple groups of different wave components during the propagation process, and showed significant spatial dispersion and structural modulation.
The research team compared the results of numerical simulations containing dispersion behavior with actual measurements from satellites and buoys and found that the consistency between this type of "dispersion model" and real observations is significantly better than simplified models that use traditional assumptions. Ruiz-Angulo pointed out that this means that the currently commonly used tsunami numerical models are "missing something" in terms of physical mechanisms, especially the internal structure and energy redistribution of large-scale tsunami wave groups are still insufficient. He further speculated that these additional dispersion energy may lead to "trailing wave" modulation before and after the main tsunami wave crest, thereby affecting local wave height and arrival sequence when approaching certain coasts. These potential effects need to be quantified and incorporated into future forecast systems.
In this study, the team also compared SWOT and DART observations with previous tsunami forecasts based on earthquake source and surface deformation data. They found that at some deep-sea monitoring sites, the traditionally predicted tsunami arrival time did not match the DART actual measurement: at one site, the arrival time given by the model was too early, while at another site, the arrival time was too late. To resolve this contradiction, researchers used the so-called "inversion" method to re-estimate the source rupture characteristics using actual buoy measurements as constraints. The results showed that the rupture zone of this 8.8-magnitude earthquake extended farther south than predicted by previous models, with a total length of approximately 400 kilometers, significantly longer than the previously estimated 300 kilometers.
Diego Melgar, co-author of the paper, pointed out that since the 9.0 magnitude earthquake off the coast of Tohoku, Japan in 2011, the seismological community has gradually realized that tsunami observation data is of great value in constraining the slip distribution of shallow faults. In recent years, researchers have been trying to integrate tsunami data such as DART with traditional seismic waves and surface deformation measurements. However, in actual operations, this type of multi-source data coupling has not yet been completely normalized. One of the important reasons is that there are major differences in the physical and computational frameworks between the fluid dynamics model that simulates tsunamis and the solid earth model that simulates seismic wave propagation. He emphasized that this study once again shows that combining a wider variety of observations is critical to understanding earthquake source characteristics and tsunami behavior.
The Kamchatka-Kurile Island Arc area is a world-famous area prone to strong earthquakes and tsunamis. As early as 1952, a major earthquake with a magnitude of 9.0 in the region triggered a tsunami across the Pacific Ocean and directly promoted the establishment of the international tsunami warning system. This system also played a key role in early warning and issuing warnings in this event in 2025.
Researchers said that as satellite observation data similar to SWOT continues to accumulate, it is expected to play a greater role in real-time or quasi-real-time tsunami forecasting in the future. Ruiz-Angulo said that if such results can be repeated in more actual events in the future, it will help prove to decision-makers and funders that investing in specialized satellite observation capabilities has long-term value in improving global tsunami monitoring and early warning levels.