Location:

Period:

30 Jun 2008 06:17:43 - 1 Jul 2008 04:04:54 (21 hours 47 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 7.0; South Sandwich Islands region; (30 Jun 2008) (10km from the swarm center)

3 swarms found nearby.

2015

PS20150526.1(198.2km)

26 May

24 minutes

5 earthquakes

2018

PS20180905.1(176.1km)

4 Sep

15 hours

7 earthquakes

2021

PS20210812.4(136.1km)

12 Aug

4 days 8 hours

53 earthquakes

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Seismic Swarm East of the South Sandwich Islands: June–July 2008

The South Sandwich Islands region lies along the southern Atlantic Ocean's active plate boundary, where the South American Plate subducts westward beneath the Scotia Plate at rates of approximately 70–80 mm per year. This subduction produces the South Sandwich Trench and fuels both intermediate-depth seismicity and arc volcanism. The tectonic setting has generated recurrent moderate-to-large earthquakes throughout recorded history, with instrumentally documented events exceeding magnitude 7 occurring multiple times per decade.

Between 06:17 UTC on 30 June and 04:04 UTC on 1 July 2008, a compact seismic swarm comprising five events was recorded east of the South Sandwich Islands. The sequence began with a magnitude 7.0 earthquake at 8 km depth, followed within roughly 22 hours by four additional shocks of magnitudes 5.1, 5.3, 5.6, and 4.8 at depths ranging from 10 km to 35 km. The largest event remains the only magnitude-7.0 earthquake in the South Sandwich Islands region since 2000 located within 10 km of the swarm centroid.

Such swarms are characteristic of the outer-rise and shallow subduction interface in this setting, where bending-related faulting and episodic slip on the plate interface can produce clustered activity over hours to days. Depths between 8 km and 35 km place the events within the seismogenic zone of the megathrust and overlying crust, consistent with the regional velocity structure derived from global and regional networks.

No significant damage or tsunami was reported from this sequence, reflecting both the remote location and the moderate magnitudes of the follow-on events. Continued monitoring by global seismic networks confirms that the South Sandwich subduction zone remains one of the most active segments of the Scotia Sea plate boundary, capable of producing both isolated great earthquakes and short-lived swarms of the type observed in 2008.

References

USGS Earthquake Catalog (ANSS Comprehensive Catalog)
Global Centroid Moment Tensor Project (GCMT)
International Seismological Centre (ISC) Bulletin