A seismic swarm at the Bransfield Rift, Antarctica

Abstract

The Brasfield rift and South Shetland trench are part of the active margin of the Antarctic continent. From the records of a seismic station at the King George Island installed by the Observatorio Geofísico del Uruguay, 3186 seismic events during August 26 and September 11, 2020 were retrieved with an average of 187 earthquakes per day and a maximum of 359 on August 30. 217 events with a local magnitude of ≥4 were well recognized and located by a single-station method. The events show that an earthquake swarm close to the South Shetland Islands and at a short hypocentral distance (~25 km) to the station occurred in August of 2020. The earthquakes in the swarm are near Orca seamount and the listric normal faults, with a ENE-WSW trend of the Bransfield Basin, suggesting their volcano and volcanotectonic origin. In addition to the swarm, several earthquakes in the same time period related to the Artigas Fault with NW-SE trend are also located, which indicates the reactivation of this structure. From all the earthquakes, a relatively high b-value (1.22) is estimated, which might suggest variable resistance for stress accumulation in the Bransfield rift.