Location:

Period:

15 Apr 2008 22:59:51 - 24 Apr 2008 05:24:15 (8 days 6 hours 24 minutes)

Volcanoes in 100km radius:

Gareloi(1km), Tanaga(46km), Takawangha(55km), Bobrof(94km)

Earthquakes:

286

12 swarms found nearby.

2006

PS20060708.1(74.5km)

8 Jul

9 hours

10 earthquakes

PS20060826.1(69.0km)

26 Aug

47 minutes

6 earthquakes

2007

PS20071219.1(79.5km)

19 Dec

19 hours

12 earthquakes

2008

S20080301.2(28.4km)

1 Mar

3 days 4 hours

82 earthquakes

VS20080416.1(8.5km)

15 Apr

3 days 6 hours

89 earthquakes

2013

S20130121.1(29.9km)

21 Jan

3 days 11 hours

62 earthquakes

2017

S20170501.2(16.3km)

30 Apr

23 days 10 hours

1627 earthquakes

S20170508.2(14.4km)

8 May

3 days 22 hours

59 earthquakes

S20170527.1(28.1km)

26 May

18 days 7 hours

298 earthquakes

2018

S20180927.1(30.0km)

27 Sep

1 day 9 hours

40 earthquakes

2020

PS20200126.1(104.5km)

26 Jan

18 hours

8 earthquakes

2026

S20260617.2(8.9km)

16 Jun

1 day 5 hours

26 earthquakes

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Seismic Swarm S20080416.1: Analysis of the April 2008 Event West of Adak, Alaska

The April 2008 seismic swarm designated S20080416.1 occurred approximately 189 km west of Adak, Alaska, in the western Aleutian Islands. This region lies within the Aleutian subduction zone, where the Pacific Plate converges with and subducts beneath the North American Plate at rates of 6–8 cm per year. The resulting compressional tectonics produce frequent shallow to intermediate-depth earthquakes along the arc.

The swarm initiated at 22:59 UTC on 15 April 2008 and concluded at 05:24 UTC on 24 April 2008, spanning 198 hours and 24 minutes. During this interval, 286 earthquakes were recorded. The first 100 events exhibited a characteristic swarm pattern: an initial magnitude 6.4 event at 11 km depth, followed by numerous aftershocks ranging from magnitude 1.9 to 6.6. Depths remained predominantly shallow, between 0 and 13 km, with the majority clustered between 1 and 8 km. Notable larger events included a magnitude 4.2 at 8 km depth shortly after the onset and a magnitude 6.6 at 13 km depth roughly seven hours into the sequence. Subsequent activity consisted of smaller-magnitude events, many below magnitude 3.0, consistent with swarm behavior rather than a classic mainshock-aftershock sequence.

Analysis of the initial 100 events reveals a rapid decay in magnitude after the two largest shocks, with 70 percent of events falling below magnitude 3.0. Depths showed limited variation, indicating activity within the upper crust above the subduction interface. This pattern aligns with known swarm dynamics in subduction settings, often linked to fluid migration or stress transfer along the plate boundary.

The western Aleutians have a well-documented history of seismic swarms and great earthquakes. Since 2000, four swarms have been identified in the broader region: two in 2006, one in 2007, and the 2008 event. The area experienced the magnitude 8.6 earthquake of 1957 and the magnitude 7.9 event of 1996, both occurring along the same subduction segment. Ongoing monitoring by the Alaska Earthquake Center and the USGS confirms persistent background seismicity driven by plate convergence.

Geological studies of the Adak region highlight the presence of the Adak Canyon and associated forearc structures that influence rupture propagation. Updated geophysical models from the past decade continue to emphasize the high seismic hazard posed by the Aleutian megathrust, with potential for magnitude 8+ events.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Alaska Earthquake Center, University of Alaska Fairbanks
Tectonic summaries of the Aleutian arc, USGS Professional Papers