Location:

Period:

19 Aug 2016 07:32:22 - 21 Aug 2016 04:28:59 (1 day 20 hours 56 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 7.4; South Georgia Island region; (19 Aug 2016) (31km from the swarm center)

3 swarms found nearby.

2004

PS20040906.1(169.5km)

6 Sep

14 hours

7 earthquakes

2016

PS20160822.1(27.1km)

22 Aug

21 hours

6 earthquakes

PS20160902.1(21.1km)

1 Sep

17 hours

5 earthquakes

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Seismic Swarm Analysis: South Sandwich Islands Region, August 2016

A notable seismic swarm occurred in the South Sandwich Islands region from 07:32 UTC on 19 August 2016 to 04:28 UTC on 21 August 2016. Over 44 hours and 56 minutes, the sequence included 26 earthquakes, beginning with a magnitude 7.4 mainshock at a depth of 10 km. Subsequent events ranged from magnitude 5.0 to 6.1, with most focal depths between 3 km and 15 km.

The swarm featured an initial cluster of moderate aftershocks within the first hours, followed by intermittent activity over the next two days. Notable later events included a magnitude 5.8 earthquake at 3 km depth on 19 August and a magnitude 6.1 event at 12 km depth on 21 August. Depths remained predominantly shallow, consistent with activity along the regional subduction interface.

The South Sandwich Islands form a volcanic arc resulting from the subduction of the South American Plate beneath the Scotia Plate at rates of approximately 70–80 mm per year. This tectonic setting produces frequent seismicity, including both interplate thrust earthquakes and shallower volcanic or crustal events. The islands themselves are young, with volcanic activity documented since the Pleistocene, and the arc lies within a remote oceanic environment characterized by high seismic hazard.

Historical records since 2000 indicate limited swarm-type sequences in this specific area, with the prior event occurring in 2004. The 2016 swarm stands out due to its association with the magnitude 7.4 mainshock located about 31 km from the swarm centroid. Strong earthquakes of this scale are infrequent but align with the region's capacity for large subduction-zone events.

Insights from the sequence suggest a classic aftershock-driven swarm following a major rupture, with rapid initial decay and persistent low-level activity. The concentration of events at shallow depths points to stress redistribution along the plate interface and possible involvement of upper-plate structures. Such patterns aid in understanding rupture dynamics in remote subduction zones where direct observation is limited.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Global CMT Catalog
Tectonic framework data from the Scotia Sea region (various peer-reviewed geophysical studies)