Mysterious 9-day seismic event was caused by a mega tsunami bouncing around inside a fjord, study reveals

Scientists have finally identified the cause of a mysterious seismic signal that shook Earth for nine consecutive days last year. It turns out that our planet was rocked by a mega tsunami trapped inside a fjord after a mountaintop collapse.

The gigantic wave, measuring 650 feet (200 meters) high, sloshed back and forth inside East Greenland's Dickson Fjord for nine days in September 2023, its movement sending seismic waves reverberating through the planet's crust.

Scientists were initially baffled by the signal. But an investigation using satellite and ground imagery eventually tracked the cause of the seismic activity to the mountain, which was destabilized by climate change melting the glacier at its base. The researchers published their findings today (Sept. 12) in the journal Science.

"When we set out on this scientific adventure, everybody was puzzled and no one had the faintest idea what caused this signal," study lead author Kristian Svennevig, a geologist at the Geological Survey of Denmark and Greenland (GEUS), said in a statement. "All we knew was that it was somehow associated with the landslide. We only managed to solve this enigma through a huge interdisciplinary and international effort."

After being picked up by seismic monitoring stations in September, two aspects of the signal puzzled scientists. Firstly, unlike higher-frequency earthquakes, it was oscillating with a 92-second interval between peaks. And secondly, it was doing this for days on end.

Scientists soon tied the possible cause to a landslide in the fjord, but to understand how it produced the signal, the scientists combined field measurements, satellite imagery and supercomputer models to reconstruct what happened.

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