Earthquake occurred around the Orca Seamount, a top volcano dormant 900 m above the seabed in Bransfield Strait, a narrow passage between the South Shetland Islands and the northwestern tip of Antarctica. In this area, the Phoenix tectonic plate is diving beneath the Antarctic continental plate, creating a network of fault zones, stretching some parts of the crust and opening cracks in others. Study co-author Simone Cesca, a seismologist at the German Geosciences Research Center GFZ in Potsdam, said: “There have been similar volcanic eruptions elsewhere on Earth, but this This is the first time we’ve seen it in Antarctica.”
Scientists at research stations on King George Island, one of the South Shetland Islands, were the first to feel the tremors of small earthquakes.
The researchers had to use data from those seismic stations, as well as data from two global satellite navigation system earth stations, to measure ground displacement. They also looked at data from more distant seismic stations and from Earth-orbiting satellites that use radar to measure displacement at ground level.
By putting these data together, the team was able to create a picture of the underlying geology that caused this massive earthquake.
The two largest earthquakes in the series were the 5.9 magnitude earthquake in October 2020 and the 6.0 magnitude earthquake in November. Following the November earthquake, seismic activity gradually waned.
Research shows that earthquakes appear to have shifted on King George Island by 11 centimeters. Only 4% of that displacement can be directly explained by the earthquake. Scientists suspect that the movement of magma into the crust is largely responsible for the dramatic displacement of the ground.
If there was an underwater eruption, it would likely have occurred at that time, the researchers added. But so far, there is no direct evidence for an eruption. To confirm that the giant volcano has erupted, scientists will have to send a research team to the strait to measure the depth of the sea floor and compare it with historical maps.
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