The Entire Earth was Mysteriously Shaking Every 90 Seconds. Now, Scientists Know Why

For nine days in September 2023, the world was rocked by mysterious seismic waves that were detected globally every 90 seconds. Earth trembled again the following month with an identical global signal, though it was shorter and less intense. Baffled by the anomalies, researchers dubbed it an “Unidentified Seismic Object.” 

Scientists have now confirmed that this literally Earth-shaking event was caused by two mega-tsunamis in Dickson Fjord, a narrow inlet in East Greenland, which were triggered by the effects of human-driven climate change according to a study published on Tuesday in Nature Communications.

Previous research had suggested a link between the strange signals and massive landslides that occurred in the fjord on September 16 and October 11, 2023, but the new study is the first to directly spot the elusive standing waves, called “seiches,” that essentially rang the planet like a giant bell.

“These seiches were triggered by megatsunamis, themselves caused by enormous landslides

plunging into the fjord,” said Thomas Monahan, a Schmidt AI in Science Fellow at the University of Oxford who led the study, in an email to 404 Media. The landslides were caused by  a glacier that had been steadily thinning due to climate change, he said. 

But how in the world can two tsunamis, even those of the mega variety, cause the whole Earth to shake every 90 seconds?

“What made this event uniquely powerful, and globally detectable, was the geometry of the fjord,” he continued. “A sharp bend near the fjord’s outlet effectively trapped the seiche, allowing it to reverberate for days. The repeated impacts of the water against the fjord walls acted like a hammer striking the Earth’s crust, creating long-period seismic waves that propagated around the globe. This unusual combination of scale, duration, and geometry made the seismic signal from these regional events strong enough to be detected worldwide.”

It may sound strange that an event with such global impacts proved so difficult to spot in observational data. Indeed, a Danish military vessel was surveying the fjord during the September event and didn’t even notice the Earth-rocking waves in its depths. But the timing of the two landslides lined up perfectly with the signals, leading to studies suggesting a link.

Monahan was on vacation when he read about the studies, and he was immediately intrigued. He and his colleagues had been working with observations from the Surface Water and Ocean Topography (SWOT) satellite, a mission launched to space in 2022 which had just the right stuff to track down the mystery waves.

“SWOT is a game-changer—it provides high-resolution, two-dimensional measurements of sea surface height, even in narrow coastal and inland waters like fjords,” Monahan said. “When I read about the seiche theory, I realized we might actually have both the data and the tools needed to test it.”

“Finding the ‘seiche in the fjord’ was super exciting, but turned out to be the easy part—I knew

where to look,” he added. “The real challenge was proving that what we saw was, in fact, a seiche and not something else.” 

The team meticulously ruled out other possible oceanographic phenomena and honed in on the size and impact of the seiche. Their results suggest that the September seiche was initially 7.9 meters (26 feet) tall, which unleashed an enormous force of approximately 500 Giga Newtons into the wall of the fjord that sent ripples throughout the globe.

The landslides that set off all this noisy sloshing were let loose by the deterioration of an unnamed glacier near the fjord. Greenland’s ice sheets and glaciers are melting at an accelerated rate due to human-caused climate change, making the island the single biggest contributor to sea level rise worldwide.  

“The progressive thinning of the glacier that led to this failure is almost certainly a consequence of anthropogenic climate change,” Monahan said. “Whether we’ll see more seismic signals like these is harder to say. The signals—and the seiches that produced them—were unusual, driven in part by the unique geometry of the fjord that allowed the standing waves to form and persist. In this sense, the seismic signals acted as a kind of canary in the coal mine, pointing to the occurrence of the tsunamis and the underlying glacier instability that caused them.”

“While these specific types of signals may remain rare, continued warming will likely increase the frequency of glacier-related landslides,” he said. “As these events become more common, especially in steep, ice-covered terrain, the risk of tsunamigenic landslides will likely grow.”

To that end, Monahan and his colleagues hope to continue developing SWOT as a keen eye-in-the-sky for elusive events such as seiches and rogue waves.   

“This study highlights how climate change is unfolding rapidly in remote regions like the

Arctic—areas that are difficult to monitor using conventional instruments such as tide gauges,” Monahan said. “Our findings show the potential of next-generation satellites, like SWOT, to fill these observational gaps.”

“Continued investment in satellite missions is essential for monitoring and responding to the impacts of climate change,” he concluded.