A weird signal was sent to seismology by the mega-landslide

First Earthquake Seismology in the Greenland fjord: Recording the Sound and Vibrations of an Unidentified UFO

On 16 September 2023, seismologists worldwide registered a weird signal emanating from eastern Greenland. Missing were the variations in frequency that typically accompany events such as earthquakes: the signal was ‘monochromatic’, resembling the ringing of a bell, and lasted nine days. It was quickly registered as a UFO, er, USO: an unidentified seismic object.

A lot of sounds and tones decay very quickly, so it’s a good idea to compare the earthquakes’ effects on the sound and vibrates of a piano to breaking your hands into a full force and removing them again.

The event triggered reports of a tsunami at a research station in Greenland’s Dickson Fjord, and scientists pinpointed the likely source: a 1.2-kilometre-high mountain peak had collapsed into a gully in the fjord. It was not clear how a long lasting reverberation could be caused by a landslide. Svennevig and his colleagues assembled an interdisciplinary team to investigate.

The people began documenting the aftermath of the landslide. They calculated that the collapse of the mountain top produced a landslide carrying some 25 million cubic metres of material, equivalent to roughly 10,000 Olympic swimming pools. The rock–ice slide at the fjord was caused by the earthen material smashing into a local glacier at the bottom of a Gully.

The seiche was 7 meters tall, had a long duration, and had a frequency of 11.45 miles per hour and a slow amplitude decay that were nearly identical to the signal from the earthquake that hit the area.

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Their work toward an answer was slow, Svennevig says. Even when they gained an understanding of what likely happened, they needed more time and data to prove it.

To the researchers, the signal was like an alarm bell — one that “rang” the Earth for nine days. They said that it is one of the most striking wakeup calls they have gotten about climate change. They warn that we could see cascading events in the future.

“We may expect similar signals to occur if a landslide should happen in a similarly shaped fjord or lake,” Svennevig says. Due to global warming, we expect the frequencies of earthquakes and floods to increase.

There is more work to be done to understand how the planet is adapting to climate change, with the mystery of the global seismic signal solved.

Precedents for such seismological signals existed in the scientific literature going back more than a decade. There had been a number of land slides in the closed water basins which produced a series of back and forth motions known as seiche. These events were only available to be registered in the local area.

It’s a nice study that explains an “extremely weird and unusual” seismological event, says Göran Ekström, a geophysicist at the Columbia University’s Lamont-Doherty Earth Observatory in Palisades, New York. He chalks it up to teamwork and the sharing of data. “The speed at which the team was able to document, describe and explain the sequence of events shows how science can work these days.”

In the end, Svennevig and his team suggests that the actual culprit was global warming, which thinned the glacier underpinning the mountain and ultimately set the stage for the landslide. He says there will probably be more funky events in the future.

A signal from a seismic event in Greenland last year that triggered a tsunami was similar to an alarm bell ringing, researchers have said. The’monochromatic’ signal was similar to the one from an earthquake that hit the area. The earthquake signal lasted for nine days with a frequency of 11.45 miles per hour and a slow amplitude decay.