NASA's "Water Surface and Ocean Terrain Surface Height Satellite" (SWOT), which is used to observe sea surface heights, unexpectedly obtained an unprecedented high-resolution observation of a huge tsunami when a strong earthquake occurred off the Kamchatka Peninsula at the end of July this year, providing the scientific community with the first detailed panoramic image of a tsunami from space.
Researchers pointed out in the latest paper published in the journal "The Seismic Record" that this observation revealed the complex details of the propagation and interaction of tsunami waves in the Pacific Basin, challenging the long-standing traditional understanding of large tsunamis that "almost no dispersion occurs and the shape remains basically intact."
On July 29, a strong earthquake with a moment magnitude of 8.8 occurred in the Sakhalin-Kamchatka subduction zone. It was the sixth largest earthquake recorded in the world since 1900 and triggered a cross-ocean tsunami in the Pacific. Angel Ruiz-Angulo of the University of Iceland and his team combined the sea surface height data obtained by SWOT with the records of the Deep Ocean Tsunami Observation Buoy (DART) deployed on the tsunami path to reconstruct the fluctuation process of this event. SWOT's observations show that tsunamis present a fine and complex wave structure in the Pacific basin, with multiple wave trains intertwined and superimposed in space, far exceeding the limited information that could be seen in the past when only a few buoys and traditional altimeters "passed along a thin line."
The SWOT satellite was jointly developed by NASA and the French National Center for Space Research and launched in December 2022. Its initial goal is to achieve global high-precision measurements of water bodies on the Earth's surface (including oceans, lakes, and rivers). Through an observation strip up to about 120 kilometers wide and high spatial resolution data, SWOT can capture the tiny fluctuations in sea surface height in a wide range of sea areas in a short time. It has previously been mainly used to study fine dynamic processes such as ocean eddies. Ruiz-Angulo said that the team originally only used SWOT data to study small-scale ocean structures, and did not expect to "happen" to catch a large-scale tsunami event, thus opening a new observation window for tsunami research.
In traditional tsunami theory, since the wavelength of a large tsunami is much larger than the depth of the ocean, such waves are usually regarded as "non-dispersive" gravity waves, that is, the overall wave shape is basically maintained during the propagation process and will not be significantly decomposed into leading waves and subsequent wave trains. However, the data obtained by SWOT this time show significant dispersion characteristics: after the main wave crest, there is a series of trailing wave trains, whose propagation and energy distribution are more consistent with the numerical simulation results that consider the dispersion effect. Based on this, the research team believes that the existing assumption that large tsunamis are simply regarded as non-dispersive waves is incomplete, and it is necessary to further incorporate dispersion-related dynamic mechanisms into forecasting and simulation models.
When comparing observations and simulations, the researchers also found that the early tsunami source model constructed using seismic wave and surface deformation data was not completely consistent with the measured records of some DART tide stations: the tsunami arrival time predicted by the model was earlier and later at the two observation points respectively. The team then conducted an inversion analysis using the DART data as a constraint to re-evaluate the spatial extent of the earthquake rupture area. The results showed that the rupture zone of the Kamchatka earthquake extended further to the south, with a total rupture length of approximately 400 kilometers, while the previous model estimated an estimated 300 kilometers.
Research co-author Diego Melgar pointed out that since the 9.0 magnitude earthquake in the Tohoku Sea of Japan in 2011, the scientific community has increasingly recognized the important value of tsunami data in constraining the distribution of shallow slip. However, due to the huge technical differences between hydrodynamic modeling of tsunami propagation and seismic wave propagation simulation of the solid earth, it is still not a common practice in the industry to systematically integrate the two types of data into the same inversion framework. This joint analysis of SWOT and DART once again shows that fully integrating multi-source observation data can help more accurately characterize the rupture process of large earthquakes and the characteristics of the tsunami triggered by it.
A major earthquake with a moment magnitude of 9.0 occurred in the Sakhalin-Kamchatka subduction zone in 1952, which triggered a huge Pacific tsunami and directly promoted the subsequent construction of an international early warning system for the entire Pacific region. This system also played a role again in the 2025 event. Ruiz-Angulo said that if high-resolution satellite observation data like SWOT can be used regularly in forecasting operations in the future, it is expected to significantly improve the accuracy and reliability of real-time or near-real-time tsunami warnings. The author of the paper believes that this "accidentally captured" huge tsunami provides a strong empirical basis for demonstrating the application value of satellite altimeters in tsunami monitoring and disaster warning.
Compiled from /ScitechDaily