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Researchers have used cutting-edge satellite technology to shed light on the global mystery of the unexplained seismic signals that 鈥渟hook the Earth鈥� for nine days.

In September 2023, scientists observed a bizarre series of global seismic signals, which appeared every 90 seconds over nine days 鈥� and then repeated a month later.

Almost a year later, two scientific studies proposed that the cause of these seismic anomalies were two mega tsunamis which were triggered in a remote East Greenland fjord by two major landslides which occurred due to warming of an unnamed glacier. The waves were thought to have become trapped in the fjord system, forming standing waves (or seiches) that undulated back and forth, causing the mystery signals.

Until now, there have been no observations of these seiches to confirm this theory.

Now, using a brand-new type of satellite altimetry, a team of researchers have confirmed the theory and provided the first observations of these waves whose behaviour is entirely unprecedented.

The new research is published today in the journal .

, Lecturer in Fluid Mechanics at The University of Manchester, who carried out the research in Oxford, said: 鈥淚t's impressive to see that machine learning plays an important role in identifying these trapped waves. This research demonstrates how advancements in technology are enabling new observations and datasets, and also importantly, changing our approach to extracting scientific insights from large-scale data.鈥�

Using data from the Surface Water and Ocean Topography (SWOT) satellite, the research team were able to capture the wave activity for the first time. SWOT launched in December 2022 to map the height of water across 90% of Earth鈥檚 surface. It is equipped with the cutting-edge Ka-band Radar Interferometer (KaRIn) instrument, which uses two antennas to measure ocean and surface water levels across a swath 30 miles wide.

The researchers then made elevation maps of the Greenland Fjord at various time points following the two tsunamis. These showed clear, cross-channel slopes with height differences of up to two metres. Crucially, the slopes in these maps occurred in opposite directions, showing that water moved backwards and forwards across the channel.

To validate their findings, the researchers linked these observations to small movements in the Earth鈥檚 crust recorded thousands of kilometres away, allowing them to reconstruct the characteristics of the wave, even for periods which the satellite did not observe. They also reconstructed weather and tidal conditions to rule out alternative explanations such as wind or tides.

Lead author (DPhil student, Department of Engineering Science, University of Oxford) said: 鈥淐limate change is giving rise to new, unseen extremes. These extremes are changing the fastest in remote areas, such as the Arctic, where our ability to measure them using physical sensors is limited. This study shows how we can leverage the next generation of satellite earth observation technologies to study these processes.

鈥淪WOT is a game changer for studying oceanic processes in regions, such as fjords, which previous satellites struggled to see into.鈥�

Co-author (Department of Engineering Science, University of Oxford) said: 鈥淭his study is an example of how the next generation of satellite data can resolve phenomena that has remained a mystery in the past. We will be able to get new insights into ocean extremes such as tsunamis, storm surges, and freak waves. However, to get the most out of these data we will need to innovate and use both machine learning and our knowledge of ocean physics to interpret our new results.鈥�

This research was published in the journal

Full title: Observations of the seiche that shook the world

DOI: 10.1038/s41467-025-59851-7