The mystery of the Earth's 9 consecutive days of shaking

Earth was shaken continuously for 9 days 2 years ago. Photo: Live Science .

For nine consecutive days in September 2023, the world was shaken by mysterious seismic waves that occurred every 90 seconds. The phenomenon continued a month later, but was shorter and less intense, and was dubbed “Unidentified Seismic Object”.

Now, according to a study published June 3 in the journal Nature Communications, scientists have confirmed that the earth-shaking event was actually the result of two megatsunami waves that occurred in Dickson Fjord, a fjord in East Greenland. The main cause was the effects of human-caused climate change.

A large ice sheet behind the fjord melted, causing landslides in the fjord. Ground and satellite imagery have traced the landslides, showing that they created large waves, known as seiche (standing waves).

Huge waves, some as high as 200 metres, crash into Dickson Bay. With its narrow, sharp bend near the mouth of the bay, it acts like a circular pan holding water in its centre. The trapped water oscillates constantly, crashing against the bay walls with such force that the seismic signal can be heard around the world.

A Danish military ship surveying the bay during the event failed to detect the underlying cause. Coincidentally, the strange seismic signal occurred at the same time as large-scale landslides in the bay, leading to research suggesting a link between the two.

Thomas Monahan, a Schmidt AI in Science Fellow at the University of Oxford and the project’s lead author, was working with data from the SWOT satellite, which is due to launch in December 2022 as a collaboration between NASA and CNES, the French space agency.

SWOT uses a device called KaRIn to map 90 percent of the ocean's surface water, and is key to Monahan's research. The instrument provides high-resolution, two-dimensional measurements of sea level elevation, allowing it to verify whether standing waves are the cause.

SWOT satellite sea level elevation data of Dickson Bay. Photo: Thomas Monahan.

The team carefully ruled out other possible oceanographic phenomena and focused on analyzing the size and impact of the wave. The results showed that the initial wave in September was about 7.9 m high, generating a huge force of about 500 Giga Newtons (GN) on the bay wall. From there, aftershocks spread across the globe.

The phenomenon stems from a nearby unnamed glacier that is in retreat. Greenland's ice sheets and glaciers are melting at an accelerating rate due to climate change, leading to global sea level rise.

“Climate change is causing extreme events to occur for the first time,” Monahan said. As these events become more common, especially in steep, ice-covered terrain, the risk of tsunami-triggering landslides is likely to increase.

So he and his colleagues hope to continue developing the SWOT satellite as an “eye in the sky” to detect elusive phenomena. Co-author Thomas Adcock, professor of engineering sciences at the University of Oxford, said the study is an example of how the next generation of satellite data could decipher phenomena that were previously mysterious.

“We will be able to better understand extreme ocean events such as tsunamis, storm surges and anomalous waves. However, to make the most of this data, we need to innovate and combine both machine learning and ocean physics to explain the new results,” he added.

Source: https://znews.vn/bi-an-rung-chan-lien-tiep-9-ngay-cua-trai-dat-post1558127.html