Seismic Swarm Activity in the South Sandwich Islands Region, June 2014

The South Sandwich Islands region forms part of an active subduction zone where the South American plate descends beneath the Scotia plate. This tectonic setting produces frequent moderate-to-large earthquakes at shallow to intermediate depths, along with arc volcanism that has built the island chain. Subduction rates average 70–80 mm per year, sustaining one of the most seismically active segments of the southern Atlantic.

On 29 June 2014 a seismic swarm (internal designation PS20140629.1) was recorded in the region. The sequence began at 07:52 UTC and concluded at 17:33 UTC, spanning 9 hours 40 minutes and comprising 11 events. Magnitudes ranged from 4.4 to 6.9, with the majority occurring at depths of 6–16 km and one deeper event at 60 km. The largest shock (M 6.9) initiated the swarm, followed within minutes by an M 5.2 event. Subsequent activity included three M 5.1 shocks clustered around 08:21–08:29 UTC, an M 5.8 at 14:20 UTC, and an M 6.0 at 14:32 UTC. The final recorded event was an M 5.1 at 17:33 UTC.

Such swarms reflect episodic stress release along the plate interface or within the overriding plate, commonly observed in subduction environments. No damage or tsunami reports were associated with this sequence, consistent with the remote oceanic location.

Since 1 January 2000 the same region has experienced two prior swarms, one in 2004 and one in 2010. The 2014 swarm therefore represents the third documented swarm episode in the instrumental record for this source zone.

References

USGS Earthquake Catalog (ANSS Comprehensive Catalog)
Global CMT Project focal-mechanism database
South Sandwich Islands tectonic summaries, NOAA National Centers for Environmental Information