Carlini’s base on King George Island, where the seismometer closest to the seismic region and the Bransfield Strait are located. Credit: Milton Percy Placencia Linares
In a remote area, a combination of geophysical methods identified magma transport below the seabed as the cause.
Volcanoes can even be found off the coast of Antarctica. A series of more than 85,000 earthquakes were recorded in 2020 in the deep-sea volcano Orca, which has been inactive for a long time, a swarm earthquake that has reached unprecedented proportions for the region. The fact that such events can be studied and described in remarkable detail, even in such remote and therefore poorly equipped areas, is now shown by a study by an international team published in the journal Communications Earth and Environment.
Researchers from Germany, Italy, Poland and the United States were included in the study, which was led by Simon Ceska of the German Geosciences Research Center (GFZ) Potsdam. They were able to combine seismological, geodetic and remote sensing techniques to determine how the rapid transfer of magma from the Earth’s mantle near the mantle crust boundary almost to the surface caused a swarm earthquake.
Volcano Orca between the top of South America and Antarctica
Swarms occur mainly in volcanically active regions. Therefore, it is assumed that the cause is the movement of fluids in the earth’s crust. The Orca Underwater Shield is a large underwater shield volcano about 900 meters above sea level and a base diameter of about 11 kilometers. It is located in the Bransfield Strait, an ocean channel between the Antarctic Peninsula and the South Shetland Islands, southwest of the southern tip of Argentina.
Illustration of the seismically active zone near Antarctica. Credit: Cesca et al. 2022; Nature Commun Earth Environ 3, 89 (2022); doi.org/10.1038/s43247-022-00418-5 (CC BY 4.0)
“In the past, seismicity in the region was moderate. However, in August 2020, an intense seismic swarm began there with more than 85,000 earthquakes in half a year. This is the largest seismic disturbance ever recorded there, “said Simon Ceska, a scientist in section 2.1 of the GFZ on the physics of earthquakes and volcanoes and lead author of the study. Simultaneously with the swarm on the neighboring island of King George, a lateral displacement of the earth of more than ten centimeters and a small rise of about one centimeter was registered.
Challenges of research in a remote area
Cesca is studying these events with colleagues from the National Institute of Oceanography and Applied Geophysics – OGS and the University of Bologna (Italy), the Polish Academy of Sciences, Leibniz University in Hanover, the German Aerospace Center (DLR) and the University of Potsdam. The challenge was that there were few conventional seismological instruments in the remote area, namely only two seismic and two GNSS stations (ground stations of the Global Navigation Satellite System that measure ground displacement). To reconstruct the chronology and development of the waves and determine their cause, the team further analyzed data from more distant seismic stations and data from InSAR satellites that use radar interferometry to measure ground displacement. An important step was modeling events with a number of geophysical methods to interpret the data correctly.
Reconstruction of seismic events
Researchers date the unrest to August 10, 2020, and expand the original global seismic catalog, which contains only 128 earthquakes, to more than 85,000 events. The swarm reached its peak with two major earthquakes on October 2 (Mw 5.9) and November 6 (Mw 6.0) 2020, before subsiding. By February 2021, seismic activity had decreased significantly.
Scientists have identified magma penetration, the migration of larger volumes of magma, as the main cause of the swarm earthquake, as seismic processes alone cannot explain the strong surface deformation observed on King George Island. The presence of volumetric penetration of magma can be confirmed independently on the basis of geodetic data.
Beginning in origin, seismicity first migrates upward and then laterally: deeper, grouped earthquakes are interpreted as a response to the vertical spread of magma from a reservoir in the upper mantle or at the crust-mantle boundary, while shallower earthquakes are interpreted. extending to the north-southwest is triggered at the top of the laterally growing magma dike, which reaches a length of about 20 kilometers.
Seismicity declined sharply by mid-November, after about three months of prolonged activity, in line with the largest earthquakes in the series, with a magnitude of Mw 6.0. The end of the swarm can be explained by the loss of pressure in the magma dike accompanying the sliding of a large fault and may mark the time of the eruption of the seabed, which, however, can not yet be confirmed by other data.
By modeling GNSS and InSAR data, the scientists calculated that the volume of Bransfield magmatic intrusion was in the range of 0.26-0.56 km³. This makes this episode and the biggest magmatic disturbance ever observed in Antarctica.
Conclusion
Simone Ceska concludes: “Our study is a new successful study of seismic volcanic waves in a remote place on Earth, where the combined application of seismology, geodesy and remote sensing techniques is used to understand earthquake processes and magma transport in poor equipment. areas. This is one of the few cases in which we can use geophysical instruments to monitor the penetration of magma from the upper mantle or the crust-mantle boundary into the shallow crust – rapid transfer of magma from the mantle to almost the surface, which takes only a few days.
Reference: “Massive earthquake caused by magmatic intrusion in the Bransfield Strait, Antarctica” by Simone Ceska, Monica Sugan, Lukasz Rudzinski, Sanas Wadzhedian, Peter Nimetz, Simon Planck, Geza Petersen, Jiguo Deng, Eleanzora Rivalta Plasencia Linares, Sebastian Heimann and Torsten Dahm, 11 April 2022, Communications Earth & Environment.DOI: 10.1038 / s43247-022-00418-5
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