Location:

Period:

12 Mar 2016 02:39:21 - 14 Mar 2016 07:28:05 (2 days 4 hours 48 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

12 swarms found nearby.

2008

S20081031.1(18.4km)

31 Oct

3 days 18 hours

94 earthquakes

PS20081031.1(29.7km)

31 Oct

1 day 9 hours

6 earthquakes

2013

PS20130831.1(68.1km)

31 Aug

15 hours

5 earthquakes

PS20130904.2(43.0km)

4 Sep

1 day 7 hours

11 earthquakes

S20130905.1(29.7km)

4 Sep

6 days 6 hours

96 earthquakes

S20130906.1(15.9km)

5 Sep

2 days 8 hours

36 earthquakes

2015

PS20150905.1(24.8km)

4 Sep

18 hours

5 earthquakes

S20150905.1(28.0km)

5 Sep

2 days 11 hours

103 earthquakes

PS20151102.1(55.8km)

2 Nov

15 minutes

5 earthquakes

2016

S20160319.1(19.1km)

18 Mar

3 days 15 hours

59 earthquakes

PS20160319.1(19.0km)

18 Mar

15 hours

5 earthquakes

2022

S20221029.1(20.3km)

28 Oct

2 days 4 hours

39 earthquakes

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Seismic Swarm S20160312.2: Earthquake Activity Southeast of Atka, Alaska

The seismic swarm designated S20160312.2 occurred 91 km south-southeast of Atka, Alaska, within the tectonically active Aleutian subduction zone. The sequence began at 02:39 UTC on 12 March 2016 and concluded at 07:28 UTC on 14 March 2016, spanning 52 hours and 48 minutes. During this period, 52 earthquakes were recorded, providing a detailed snapshot of transient seismic energy release along the plate interface.

The Aleutian Islands form part of the Aleutian Arc, where the Pacific Plate subducts beneath the North American Plate at rates of approximately 6–7 cm per year. This convergent margin produces frequent earthquakes and volcanism, with the region near Atka characterized by intermediate-depth seismicity and shallow crustal events associated with volcanic systems such as Korovin Volcano. Historical records indicate elevated seismic productivity, including great earthquakes such as the 1957 Mw 8.6 Andreanof Islands event and the 1986 Mw 8.0 event, both occurring along nearby segments of the arc.

Analysis of the swarm reveals a mainshock of magnitude 5.6 at 13:23 UTC on 12 March, located at a depth of 12 km. Subsequent events included four additional earthquakes of magnitude 4.0 or greater, with the deepest event reaching 43 km on 13 March. Magnitudes ranged from 1.9 to 5.6, and focal depths clustered primarily between 5 and 25 km, consistent with activity near the subduction interface and overlying crust. The temporal pattern shows peak activity within the first 24 hours, followed by a gradual decline, typical of swarm behavior driven by fluid migration or stress triggering rather than a single mainshock-aftershock sequence.

Depth variations suggest involvement of both shallow crustal processes and deeper slab-related fracturing. Shallow events (under 10 km) may reflect volcanic or hydrothermal influences, while mid-crustal events align with the expected seismogenic zone in this segment of the arc.

Since 1 January 2000, nine swarms have been documented in the broader region. Earlier episodes occurred in 2008 (two swarms), 2013 (four swarms), and 2015 (three swarms), indicating recurring episodic unrest. These events underscore the persistent seismic hazard in the central Aleutians, where monitoring supports both tectonic research and volcanic risk assessment.

This swarm contributes to understanding short-term clustering in subduction zones. Continued instrumentation by regional networks aids in refining models of stress accumulation and release along the arc.

References

USGS Earthquake Catalog (ANSS Comprehensive Catalog)
Alaska Earthquake Center, University of Alaska Fairbanks
Alaska Volcano Observatory, USGS
Global CMT Catalog for focal mechanism context