Location:

Period:

2 Nov 2015 08:15:33 - 2 Nov 2015 08:31:15 (15 minutes)

Volcanoes in 100km radius:

Seguam(98km)

Earthquakes:

17 swarms found nearby.

2008

S20080304.1(73.2km)

4 Mar

1 day 5 hours

42 earthquakes

S20081031.1(74.0km)

31 Oct

3 days 18 hours

94 earthquakes

PS20081031.1(77.4km)

31 Oct

1 day 9 hours

6 earthquakes

2011

PS20110628.1(110.1km)

27 Jun

16 hours

7 earthquakes

2013

PS20130831.1(116.1km)

31 Aug

15 hours

5 earthquakes

PS20130904.2(90.0km)

4 Sep

1 day 7 hours

11 earthquakes

S20130905.1(82.0km)

4 Sep

6 days 6 hours

96 earthquakes

S20130906.1(71.4km)

5 Sep

2 days 8 hours

36 earthquakes

S20130914.2(101.1km)

14 Sep

3 days 10 hours

87 earthquakes

2015

S20150904.1(112.7km)

4 Sep

1 day 9 hours

45 earthquakes

PS20150905.1(77.4km)

4 Sep

18 hours

5 earthquakes

S20150905.1(79.8km)

5 Sep

2 days 11 hours

103 earthquakes

2016

S20160312.2(55.8km)

12 Mar

2 days 4 hours

52 earthquakes

S20160319.1(72.9km)

18 Mar

3 days 15 hours

59 earthquakes

PS20160319.1(55.3km)

18 Mar

15 hours

5 earthquakes

2021

S20210811.1(105.4km)

10 Aug

2 days 19 hours

224 earthquakes

2022

S20221029.1(75.9km)

28 Oct

2 days 4 hours

39 earthquakes

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Seismic Swarm Event PS20151102.1 Southeast of Atka, Alaska

A seismic swarm designated PS20151102.1 occurred on 2 November 2015, approximately 103 km southeast of Atka in the Aleutian Islands, Alaska. The sequence began at 08:15 UTC and concluded at 08:31 UTC, during which five earthquakes were recorded within a 15-minute window. This event forms part of the region's well-documented tectonic activity along the Aleutian subduction zone.

The Aleutian Islands lie at the convergent boundary where the Pacific Plate subducts beneath the North American Plate at rates averaging 6–8 cm per year. This tectonic setting produces frequent earthquakes and volcanic activity characteristic of the Pacific Ring of Fire. Depths of the recorded events ranged from 10 to 13 km, consistent with intermediate-depth seismicity in the Wadati-Benioff zone associated with the subducting slab.

The individual events unfolded as follows. The initial shock at 08:15:33 registered magnitude 5.8 at 13 km depth. Subsequent shocks occurred at 08:19:49 (magnitude 4.4, 10 km), 08:24:22 (magnitude 5.1, 10 km), 08:27:48 (magnitude 5.0, 10 km), and 08:31:15 (magnitude 5.3, 10 km). All but the first event clustered at 10 km depth, indicating a compact source volume.

Historical records since 2000 show 12 swarms in the broader area. Earlier swarms took place in 2008 (three events), 2011 (one event), 2013 (five events), and 2015 (three events, including the present sequence). Such episodic clustering reflects the pulsed nature of stress release along the megathrust and associated crustal faults.

The Aleutian arc has produced several notable earthquakes in the past century, including the great 1957 Andreanof Islands event (magnitude 8.6) and the 1965 Rat Islands earthquake (magnitude 8.7). These large events underscore the potential for the subduction zone to generate both swarm activity and major ruptures. Atka itself sits on an island within the central Aleutians, near several active volcanoes whose magma systems interact with regional faulting.

Ongoing monitoring by the Alaska Earthquake Center and the U.S. Geological Survey continues to track microseismicity in this sector. The 2015 swarm, while moderate in scale, contributes to refined models of slab geometry and stress transfer in the region. No significant damage or tsunami was associated with the sequence.

References
U.S. Geological Survey Earthquake Catalog
Alaska Earthquake Center Regional Seismicity Reports
National Oceanic and Atmospheric Administration Aleutian Tectonic Summaries