Location:

Period:

8 May 2017 01:17:44 - 11 May 2017 23:30:46 (3 days 22 hours 13 minutes)

Volcanoes in 100km radius:

Gareloi(14km), Tanaga(32km), Takawangha(41km), Bobrof(80km), Kanaga(98km)

Earthquakes:

12 swarms found nearby.

2006

PS20060708.1(80.4km)

8 Jul

9 hours

10 earthquakes

PS20060826.1(79.2km)

26 Aug

47 minutes

6 earthquakes

2007

PS20071219.1(85.1km)

19 Dec

19 hours

12 earthquakes

2008

S20080416.1(14.4km)

15 Apr

8 days 6 hours

286 earthquakes

VS20080416.1(19.0km)

15 Apr

3 days 6 hours

89 earthquakes

2013

S20130121.1(18.7km)

21 Jan

3 days 11 hours

62 earthquakes

2017

S20170501.2(2.7km)

30 Apr

23 days 10 hours

1627 earthquakes

S20170508.1(23.2km)

7 May

3 days 10 hours

165 earthquakes

S20170527.1(15.8km)

26 May

18 days 7 hours

298 earthquakes

2018

S20180927.1(16.2km)

27 Sep

1 day 9 hours

40 earthquakes

2023

S20230613.1(27.4km)

13 Jun

1 day 7 hours

40 earthquakes

2026

S20260617.2(23.3km)

16 Jun

1 day 5 hours

26 earthquakes

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Seismic Swarm S20170508.2 Near Adak, Alaska: Geological Context and Event Analysis

Seismic swarm S20170508.2 occurred approximately 125 km west of Adak, Alaska, in the central Aleutian Islands. The sequence began at 01:17 on 8 May 2017 and concluded at 23:30 on 11 May 2017, spanning 94 hours and 13 minutes. During this period, 59 earthquakes were recorded, with magnitudes ranging from 1.4 to 5.0 and focal depths predominantly between 4 km and 30 km.

The Aleutian subduction zone, where the Pacific Plate converges with and subducts beneath the North American Plate at rates of 6–7 cm per year, forms the tectonic framework for this activity. This region experiences frequent seismicity due to plate interface slip, intraslab deformation, and volcanic arc processes. Adak lies within the Andreanof Islands segment of the arc, an area characterized by thrust faulting and historical great earthquakes, including the 1957 Mw 8.6 event. Depths observed in the swarm align with typical crustal and upper-mantle seismicity in the overriding plate and subducting slab.

Activity peaked on 8 May, featuring multiple events above magnitude 4.0 within a short window. Notable shocks included a magnitude 4.6 at 17:39 (depth 10 km), followed by events of 4.1, 4.5, 4.2, and 4.4 within 35 minutes, all at similar shallow depths around 10 km. The largest event, magnitude 5.0 at 19:53 (depth 10 km), occurred shortly after a magnitude 4.9 shock. Subsequent activity included a magnitude 4.7 at 20:39 and a magnitude 4.0 at 21:47. Later events on 8–11 May were smaller, generally below magnitude 3.0, with depths shifting slightly deeper on average.

This swarm represents the second such sequence recorded in 2017 in the broader Adak region. Historical data since 2000 indicate eight swarms total, with prior occurrences in 2006 (two swarms), 2007 (one), 2008 (two), and 2013 (one). Such episodic clustering is common in subduction zones and may reflect stress transfer along the plate interface or fluid migration, though individual swarm mechanisms require further modeling.

The events underscore the persistent seismic hazard in the central Aleutians. Monitoring by regional networks continues to track aftershock decay and potential recurrence patterns in this tectonically active setting.

References

USGS Earthquake Catalog
Alaska Earthquake Center Annual Reports
NOAA National Centers for Environmental Information (tectonic summaries)