The 2018 Magnitude 7.1 Earthquake in the South Sandwich Islands Region

The South Sandwich Islands region lies along a tectonically active subduction zone in the southern Atlantic Ocean. Here, the South American Plate subducts westward beneath the Scotia Plate at rates of approximately 70–80 mm per year, generating frequent intermediate-depth seismicity. The subducting slab extends to depths exceeding 200 km, producing earthquakes that reflect both brittle failure and dehydration reactions within the slab. On 11 December 2018 at 02:26 UTC, a magnitude 7.1 earthquake struck the South Sandwich Islands region at a depth of 133 km. The event occurred within the subducting slab and was followed by aftershocks consistent with intraslab deformation. No significant tsunami was generated, and impacts on the remote islands remained minimal due to the depth and offshore location. The region has hosted several strong earthquakes since 2000. The 11 December 2018 magnitude 7.1 event was followed roughly three years later by the 12 August 2021 magnitude 8.1 South Sandwich Islands earthquake, located 67 km from the 2018 hypocenter. Both events illustrate the persistent seismic productivity of the subduction interface and the Wadati-Benioff zone. Geological studies attribute the high seismicity to the steep dip of the subducting slab and the relatively young age of the incoming South American Plate lithosphere. Historical records document recurrent great earthquakes, underscoring the region’s capacity for large-magnitude events despite its isolation from major population centers.

References

USGS Earthquake Catalog Global CMT Catalog NOAA National Centers for Environmental Information