Orca volcano underwater in Antarctica swarm of 85,000 earthquakes

In the past, earthquakes in this region were moderate. However, in August 2020, an intense seismic swarm began there, with more than 85,000 earthquakes in half a year. It represents the largest seismic disturbance ever recorded there,” reports Simon Siska, a Division 2.1 volcanic and seismic scientist at GFZ and lead author of the now-published study. At the same time as the swarm occurred, the Earth had a lateral displacement of more than four inches and a small lift by about one centimeter on neighboring King George Island.

Research challenges in a remote area

Cesca studied 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 seismographs in the remote area, ie only two seismic stations and two GNSS stations (ground stations in yLopal nortiFlight sSatellites ssystem, which measures the displacement of the Earth). To reconstruct the timing and evolution of the disturbances and determine their causes, the team analyzed data from remote seismic stations and data from the InSAR satellites, which use radar interferometry to measure ground displacement. An important step was modeling the events with a series of geophysical methods to correctly interpret the data.

Reconstruction of seismic events

The researchers dated the onset of the disturbances to August 10, 2020, and expanded the original global catalog of earthquakes, which contained just 128 earthquakes, to more than 85,000 events. The swarm peaked with two major earthquakes on October 2 (Mw 5.9) and November 6 (MW 6.0) 2020 before declining. By February 2021, seismic activity had decreased significantly.

Scientists have identified magma intrusion and migration of a larger volume of magma as the main cause of the swarm earthquake, because seismic processes alone cannot explain the strong surface deformation observed on King George Island. The presence of volumetric magma intrusion can be independently confirmed on the basis of geodetic data.

Starting at their source, the earthquakes migrated first upward and then laterally: deep cluster earthquakes are interpreted as a response to the vertical spread of magma from a reservoir in the upper mantle or at the crustal mantle boundary, while those superficial crustal earthquakes extend to the northeast and run over a growing magma dam. Laterally, it reaches a length of about 20 kilometers.

The earthquakes decreased abruptly in mid-November, after nearly three months of continuous activity, coinciding with the occurrence of the largest in the series, with a magnitude of 6.0 MW. The end of the swarm can be explained by the pressure loss in the magma dam, which accompanies a large fault slip, and can indicate the time of seafloor eruption, which, however, cannot be confirmed by other data.

Using GNSS and InSAR data modeling, the scientists estimated that the volume of the magma intrusion at Bransfield ranged from 0.26 to 0.56 cubic kilometres. This also makes this ring the largest rock eruption ever observed in Antarctica.

Conclusion

Simon Siska concludes: “Our study represents a successful new investigation into seismic volcanic disturbances in a remote location on Earth, where the combined application of remote sensing, geodesic and seismic techniques is used to understand seismic processes and magma transport in Earth regions. This is one of the few cases where we can Using geophysical instruments to monitor magma penetration from the upper mantle or crustal mantle boundary to the shallow crust, a rapid transition of magma from the mantle to near the surface that takes only a few days.”

Reference: “Massive seismic swarm driven by molten intervention in Bransfield Strait, Antarctica” by Simon Cesca, Monica Sugan, Okasz Rudzinski, Sanaz Fagidian, Peter Nimes, Simon Blanc, Jessa Petersen, Ziggo Deng, Eleonora Rivalta, Alessandro Burke-van Placencia Linares, Sebastian Heymann, and Torsten Dahmy, 11 Apr 2022, Available here. Earth and Environment Communications.
DOI: 10.1038 / s43247-022-00418-5