The 2021 South Sandwich Islands Earthquake Sequence

The South Sandwich Islands region lies in the southern Atlantic Ocean along the boundary between the South American and Scotia plates. This tectonically active margin features the South Sandwich Trench, where oceanic lithosphere subducts westward, generating frequent large-magnitude earthquakes. The islands themselves form a volcanic arc resulting from this subduction process, with a history of seismic events dating back to instrumental records in the early twentieth century. On 12 August 2021 at 18:32 UTC, a magnitude 7.5 earthquake struck the South Sandwich Islands region at a depth of 47.2 km. This event occurred within a sequence that also included a magnitude 8.1 mainshock earlier the same day, located approximately 90 km away. Both earthquakes reflect the ongoing convergence along the subduction interface, where stress accumulation periodically releases in powerful ruptures. The broader seismic history of the region since 2000 demonstrates repeated strong events capable of producing regional tsunami warnings and aftershock sequences. The 2021 activity fits established patterns of intermediate-depth seismicity linked to the subducting slab. Depths around 47 km are consistent with the geometry of the Wadati-Benioff zone beneath the trench. Geological studies characterize the South Sandwich subduction zone as one of the most active in the Atlantic basin, with convergence rates supporting the occurrence of great earthquakes. The 2021 sequence underscores the persistent hazard in this remote area, where monitoring relies heavily on global seismic networks.

References

USGS Earthquake Catalog Global CMT Catalog