Seismic Swarm PS20170511.1 in the South Sandwich Islands Region

A seismic swarm designated PS20170511.1 occurred in the South Sandwich Islands region, commencing at 23:23 on 10 May 2017 and concluding at 05:21 on 12 May 2017. Over this 29-hour, 57-minute period, 16 earthquakes were recorded. The events clustered tightly in both time and location, exhibiting magnitudes from 4.9 to 6.5 and focal depths predominantly near 10 km, with isolated instances reaching 15 km, 13 km, 11 km, and 24 km.

The sequence began with a magnitude 6.5 event at 15 km depth. Subsequent activity included a magnitude 5.6 shock followed closely by a 5.4 event, both at 10 km depth. Additional events registered magnitudes of 5.0, 4.9, 5.1, 5.7, 5.3, 5.2, 5.4, 5.0, 5.1, and a final 5.1 at 10 km depth. Depths remained shallow overall, consistent with crustal deformation in an active subduction environment.

The South Sandwich Islands lie along the convergent boundary between the South American Plate and the Scotia Plate. Oceanic lithosphere of the South American Plate subducts westward beneath the Scotia Plate at the South Sandwich Trench, generating the South Sandwich volcanic arc. This tectonic configuration produces frequent intermediate-depth and shallow seismicity, with earthquake swarms often linked to fluid migration or stress transfer along the plate interface and overlying crust.

Since 1 January 2000, only two prior swarms have been identified in the region: one in 2010 and another in 2014. A magnitude 7.2 earthquake struck on 28 May 2016 approximately 84 km from the swarm center, underscoring the area’s capacity for significant events. The 2017 swarm did not feature a dominant mainshock followed by decaying aftershocks; instead, energy release occurred in a compact temporal window without clear migration patterns.

Such swarms contribute to understanding stress accumulation and release along the subduction zone. Continued monitoring refines models of plate coupling and volcanic-seismic interactions in this remote yet tectonically active segment of the Scotia Sea.

References

USGS Earthquake Catalog (historical events and magnitudes).
Global CMT Catalog (focal mechanisms and depths).
Scientific literature on Scotia Plate tectonics (subduction dynamics).