The 2016 Magnitude 7.2 Earthquake in the South Sandwich Islands Region

The South Sandwich Islands region lies in the southern Atlantic Ocean along the Scotia Arc, a tectonically active boundary where the South American Plate subducts westward beneath the Scotia Plate. This subduction zone drives the formation of the South Sandwich Trench and associated volcanic islands, producing intermediate-depth seismicity due to slab dehydration and phase changes within the descending lithosphere. The regional geology features a narrow forearc, back-arc spreading in the Scotia Sea, and a history of arc volcanism dating back several million years, with ongoing plate convergence rates estimated at approximately 6–7 cm per year.

On 28 May 2016 at 09:46 UTC, a magnitude 7.2 earthquake occurred in the South Sandwich Islands region at a focal depth of 78 km. The event was centered within the subducting slab, consistent with the typical depth range for intraslab earthquakes in this subduction setting. According to records of strong earthquakes since 1 January 2000, this remains the sole magnitude 7.2 event in the immediate vicinity, highlighting its significance within the local seismic catalog.

The earthquake’s depth and location suggest rupture along a steeply dipping fault plane within the subducted oceanic crust, a common mechanism in cold, mature subduction zones like the South Sandwich system. No significant tsunami was generated, owing to the intermediate depth and lack of substantial vertical seafloor displacement. Post-event analyses confirmed aftershock sequences clustered along the slab interface, providing further constraints on the stress regime and slab geometry in this remote sector of the Scotia Arc.

Seismic hazard assessments for the South Sandwich Islands emphasize the potential for both intraslab and interface events, given the region’s position at the junction of major plates. Historical seismicity patterns indicate recurrent moderate-to-large earthquakes driven by the same subduction dynamics that have shaped the islands’ volcanic landscape over geologic time.

References USGS Earthquake Catalog (event parameters and regional seismicity) Global CMT Project (focal mechanism and depth validation) NOAA National Centers for Environmental Information (bathymetric and tectonic context)