Location:

Period:

5 Aug 2008 22:34:03 - 21 Aug 2008 08:45:44 (15 days 10 hours 11 minutes)

Volcanoes in 100km radius:

Kasatochi(7km), Koniuji(24km), Great Sitkin(46km), Moffett(91km), Atka Volcanic Complex(92km)

Earthquakes:

1433

4 swarms found nearby.

2008

PS20081031.1(103.9km)

31 Oct

1 day 9 hours

6 earthquakes

2013

PS20130831.1(77.9km)

31 Aug

15 hours

5 earthquakes

PS20130904.2(92.7km)

4 Sep

1 day 7 hours

11 earthquakes

2015

PS20150905.1(112.2km)

4 Sep

18 hours

5 earthquakes

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Seismic Swarm VS20080806.1 in the Aleutian Islands: Geological Context and Event Analysis

The seismic swarm designated VS20080806.1 occurred approximately 85 km east-northeast of Adak, Alaska, within the tectonically active Aleutian arc. This region forms part of the convergent boundary where the Pacific Plate subducts beneath the North American Plate at rates of about 6–7 cm per year, generating frequent earthquakes and volcanic activity. The swarm initiated at 22:34 UTC on 5 August 2008 and concluded at 08:45 UTC on 21 August 2008, spanning roughly 370 hours and registering 1,433 earthquakes according to internal SeismoSight classifications.

Adak lies in the central Aleutian Islands, an area characterized by complex faulting associated with the subduction zone. Historical seismicity includes major events such as the 1956 magnitude 8.6 Andreanof Islands earthquake and numerous moderate-to-large quakes linked to the arc's volcanic centers. The local geology features a mix of sedimentary, volcanic, and metamorphic rocks shaped by millions of years of plate convergence, with nearby stratovolcanoes contributing to the region's elevated seismic hazard.

Analysis of the first 100 events reveals predominantly low-magnitude activity. Magnitudes ranged from 1.3 to 2.9, with the majority clustered between 1.4 and 2.1. Depths were shallow, typically 4–13 km, though occasional events reached 19–23 km. Timing showed rapid succession on 6 August 2008, with multiple events per hour during peak periods. These characteristics align with swarm behavior driven by fluid migration or stress adjustments along the subduction interface rather than a single mainshock-aftershock sequence.

Such swarms are common in the Aleutians due to the dynamic interplay of plate motion, volcanic processes, and hydrothermal systems. Monitoring by networks including the Alaska Earthquake Center provides ongoing data for hazard assessment in this remote but strategically important area. Continued observation helps refine models of subduction zone dynamics and supports preparedness for larger events.

References

USGS Earthquake Catalog
Alaska Volcano Observatory reports
SeismoSight internal swarm classification data