The swarm was located near the underwater volcano Orcar, which was previously considered inactive. Researchers reported about 120 events above 4 magnitude, while the two largest earthquakes – which occurred on October 2 and then on November 6, 2020 – reached magnitude 5.9 and magnitude 6, respectively. Earthquake activity has finally declined since February 2021.
This is the first time such a swarm of energy has been recorded in the region. Thanks to the combined use of seismological, geodetic and remote sensing techniques, an international team of researchers was able to determine how the rapid rise of magma from the Earth’s crust, almost reaching the surface, created this swarm. Their research has just been published in a journal Communication earth and environment.
75,000 earthquakes in six months
Seismic swells usually occur in active areas of the volcano. The movement of fluids within the Earth’s crust is therefore suspected to be the origin of the flocks observed in Antarctica. And for good reason: the region has a large underwater volcano at the bottom of the ocean, called the Orca, with an elevation of about 900 meters and a basal diameter of about 11 kilometers. ” In the past, earthquakes in this region were moderate. However, in August 2020, a series of strong earthquakes started there, with more than 85,000 earthquakes in six months. This was reported by Simon Sesca, a seismologist at the German Center for Geological Research in Potsdam, who led the study.
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Simultaneously with this earthquake activity, a lateral displacement of land (northwest) of more than ten centimeters and a weak rise of about one centimeter was recorded on neighboring King George’s Island – the largest island in the world. The South Shetland Islands, where research center workers felt the quake.
It is noteworthy that such phenomena can be described in such detail, even when they relate to isolated regions, which are poorly used. There are only two seismic stations in the area, as well as two GNSS stations (Satellite system on global) To measure displacement in the ground.
In order to reconstruct the chronology and evolution of events and then to determine the cause, the team relied on data from more distant seismic stations and Insar satellites, which measured ground displacement by radar interferometry. A series of computer modeling data helped to better explain.
A) Globe showing the location of the study area. B) Regional map showing tectonic framework (red circle indicates swarm position). C) Map of the Brainfield Basin, between the Shetland Islands and the Antarctic Peninsula. The red arrows indicate the speed and direction of ground motion. D) Local maps showing bathmetric details and adjacent areas of cement orca. Credit: S. Cesca et al., Communications Earth & Environment (2022)
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Note that in this region, the Phoenix tectonic plate is sinking beneath the continental Antarctic plate, expanding parts of the Earth’s crust and causing errors elsewhere. This subduction zone was very large in the past – it gave birth to the South Shetland Islands – but its activity slowed down considerably about 4 million years ago, when the Phoenix Plate disappeared completely beneath the Antarctic Plate, leaving only a small remnant.
A swarm caused by the penetration of a large magma
Thanks to their analysis, researchers have identified a magma penetration as the main cause of this series of earthquakes. Indeed, the strong surface deformation observed on King George’s Island cannot explain seismic processes alone (only 4% of this displacement can be explained by direct earthquakes). ” Similar intrusions have occurred in other parts of the world, but this is the first time we have seen it there. “It simply came to our notice then Live Science.
Earthquake activity shifts first from its place of origin, then to the next: Deeper and more concentrated earthquakes are interpreted as a reaction to the vertical expansion of magma from a reservoir in the Earth’s crust or boundary between the crust. The mantle crystal earthquake spreads from northeast to southwest; They were triggered by a laterally extended magma dyke. ” Sliding earthquakes indicate penetration at depth, while shallow normal errors indicate lateral growth of a dyke about 20 km long. Researchers summarize their research.
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Models based on GNSS and InSAR data suggest a magma penetration of 0.26 to 0.56 km³, making this phenomenon the largest magnetic instability observed in Antarctica. ” Typically, these processes occur on a geological time scale. So one way we are lucky to see this Cesca Conclusion.
After three months of continuous activity, the magnitude of the earthquake suddenly decreased in mid-November, shortly after the largest earthquake in the series with a magnitude of 6.0. This indicates that this strong earthquake probably caused cracks which reduced the pressure of the magnetic dyke. ” An ocean floor eruption is likely, but is not confirmed by sea surface temperature inconsistencies Researchers do not yet know if the Orca volcano erupted: the only way to verify this is to send a mission to measure the depth of the ocean floor and compare it with previous data.