Location:

Period:

26 May 2017 07:41:57 - 13 Jun 2017 14:44:12 (18 days 7 hours 2 minutes)

Volcanoes in 100km radius:

Gareloi(28km), Tanaga(30km), Takawangha(36km), Bobrof(72km), Kanaga(90km)

Earthquakes:

298

13 swarms found nearby.

2006

PS20060708.1(78.1km)

8 Jul

9 hours

10 earthquakes

PS20060826.1(82.4km)

26 Aug

47 minutes

6 earthquakes

2007

PS20071219.1(82.3km)

19 Dec

19 hours

12 earthquakes

2008

S20080416.1(28.1km)

15 Apr

8 days 6 hours

286 earthquakes

VS20080416.1(28.9km)

15 Apr

3 days 6 hours

89 earthquakes

2012

S20120927.1(24.7km)

26 Sep

10 days 9 hours

594 earthquakes

S20121018.1(28.9km)

17 Oct

3 days 8 hours

60 earthquakes

2013

S20130121.1(3.8km)

21 Jan

3 days 11 hours

62 earthquakes

2017

S20170501.2(16.0km)

30 Apr

23 days 10 hours

1627 earthquakes

S20170508.1(10.5km)

7 May

3 days 10 hours

165 earthquakes

S20170508.2(15.8km)

8 May

3 days 22 hours

59 earthquakes

2018

S20180927.1(5.3km)

27 Sep

1 day 9 hours

40 earthquakes

2023

S20230613.1(16.1km)

13 Jun

1 day 7 hours

40 earthquakes

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Seismic Swarm S20170527.1 Near Adak, Alaska: Geological Context and Event Analysis

The Aleutian subduction zone, where the Pacific Plate converges with the North American Plate at rates of approximately 6–8 cm per year, forms one of the most seismically active regions on Earth. This tectonic setting underlies the Andreanof Islands, including the area 125 km west-southwest of Adak, Alaska, and produces frequent earthquakes, volcanic arcs, and occasional earthquake swarms driven by fluid migration or stress transfer along the megathrust interface.

Swarm S20170527.1 began at 07:41 on 26 May 2017 and concluded at 14:44 on 13 June 2017, spanning 439 hours and registering 298 earthquakes. The sequence occurred within the shallow portion of the subduction zone, consistent with typical depths of 4–25 km observed in the first 100 events. Magnitudes ranged from 1.6 to 3.7, with the largest events (3.5–3.7) recorded on 27 and 28 May. Depths clustered predominantly between 4 and 14 km, indicating activity along or above the plate interface rather than deeper intraslab sources.

Temporal analysis of the initial 100 events reveals a rapid onset with multiple events exceeding magnitude 2.0 within the first 24 hours, followed by a gradual decline in frequency after 29 May. Notable peaks include three events of magnitude 3.5–3.7 on 27–28 May at depths of 7–13 km. The swarm exhibited classic characteristics of a non-mainshock-aftershock sequence, lacking a single dominant event and instead showing distributed energy release across numerous moderate-magnitude quakes.

Historical records document 11 comparable swarms in the same region since 2000, occurring in 2006 (two swarms), 2007 (one), 2008 (two), 2012 (two), 2013 (one), and 2017 (three). These episodes underscore the recurrent nature of swarm activity along this segment of the Aleutian megathrust, likely influenced by episodic fluid release from the subducting slab.

The 2017 swarm did not exceed magnitude 4.0 and produced no reported damage, aligning with background seismicity patterns in the Andreanof Islands. Continued monitoring remains essential given the zone’s potential for great earthquakes, as demonstrated by the 1957 magnitude 8.6 Andreanof Islands event.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Alaska Earthquake Center (aeic.alaska.edu)
SeismoSight internal swarm classification data