Location:

Period:

27 Aug 2019 23:55:19 - 28 Aug 2019 20:19:59 (20 hours 24 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 7.3; South Sandwich Islands region; (15 Jul 2013) (86km from the swarm center)

5 swarms found nearby.

2021

PS20210812.2(95.7km)

12 Aug

2 days 7 hours

41 earthquakes

PS20210816.1(101.4km)

15 Aug

4 days 8 hours

20 earthquakes

PS20210823.1(117.5km)

22 Aug

19 hours

8 earthquakes

PS20210827.1(135.3km)

27 Aug

1 day 6 hours

7 earthquakes

PS20210909.1(197.9km)

9 Sep

11 hours

5 earthquakes

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Earthquake Swarm PS20190828.1 in the South Sandwich Islands Region

The South Sandwich Islands region lies in the southern Atlantic Ocean along the South Sandwich subduction zone, where the South American Plate descends beneath the Scotia Plate. This tectonic setting produces frequent seismicity, including both shallow thrust events and deeper intraslab earthquakes, as well as volcanic activity along the island arc. The islands themselves are volcanic in origin, formed by magma generated from the subducting slab.

Seismic monitoring indicates that the area has hosted several moderate-to-large earthquakes in recent decades. One notable event was the magnitude 7.3 earthquake of 15 July 2013, centered approximately 86 km from the epicentral area of the 2019 swarm. Such events underscore the persistent strain accumulation and release along the plate boundary.

Between 23:55 UTC on 27 August 2019 and 20:19 UTC on 28 August 2019, a swarm of eight earthquakes was recorded in the South Sandwich Islands region. The sequence began with a magnitude 6.6 event at 16 km depth. Subsequent events included a magnitude 5.6 at 10 km depth, a magnitude 5.5 at 10 km depth, a magnitude 5.3 at 10 km depth, a magnitude 4.8 at 10 km depth, a magnitude 5.1 at 10 km depth, and two magnitude 5.1 events near the end of the sequence, one at 10 km depth and one at 60 km depth. The entire swarm lasted 20 hours and 24 minutes.

This temporal clustering of events with magnitudes between 4.8 and 6.6, concentrated at shallow to intermediate depths, is consistent with stress transfer along the subduction interface or within the overriding plate. The progression from the initial larger shock to smaller aftershocks suggests a mainshock-aftershock pattern typical of tectonic swarms in subduction settings.

No damage or tsunami impacts were reported from this sequence, reflecting both the remote location and the moderate magnitudes involved. Continued monitoring of the South Sandwich subduction zone remains important for understanding regional seismic hazards.

References

USGS Earthquake Catalog
SeismoSight internal swarm classification PS20190828.1