The 2021 M7.1 Earthquake in the South Sandwich Islands Region

On 22 August 2021 at 21:33 UTC, a magnitude 7.1 earthquake struck the South Sandwich Islands region at a shallow depth of 6.0 km. The event originated directly within the source area of prior regional seismicity and produced no reported damage due to its remote oceanic location. The South Sandwich Islands lie along the southern boundary of the Scotia Plate, where the South American Plate subducts westward beneath it at rates of approximately 5–7 cm per year. This convergent margin forms the South Sandwich Trench and drives the region’s high seismicity. The shallow focal depth of the 2021 event is consistent with rupture along the plate interface or within the overriding Scotia Plate. Seismic records since 2000 document several comparable events in the same segment of the margin. A magnitude 7.3 earthquake occurred on 15 July 2013 roughly 64 km from the 2021 epicenter, also at shallow depth. Both shocks reflect the ongoing release of strain accumulated through subduction. The tectonic framework of the Scotia Plate has evolved over the past 30 million years through the eastward migration of the South Sandwich subduction zone. This process has produced back-arc spreading in the East Scotia Ridge and frequent moderate-to-large earthquakes. Historical catalogs show that the South Sandwich region experiences magnitude 7+ events roughly every decade, underscoring its status as one of the more active subduction segments in the South Atlantic. No significant aftershock sequence or tsunami was generated by the 2021 mainshock, consistent with its moderate size and depth. Ongoing monitoring by global seismic networks continues to track strain accumulation along the plate boundary.

References

USGS Earthquake Catalog (events 2013-07-15 and 2021-08-22)
Global CMT Catalog
Bird, P. (2003). An updated digital model of plate boundaries. Geochemistry, Geophysics, Geosystems.