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Location:
92 km W of Adak, Alaska
Period:
12 Dec 2022 12:34:22 - 22 Dec 2022 23:45:03 (10 days 11 hours 10 minutes)
Volcanoes in 100km radius:
Takawangha(2km), Tanaga(10km), Bobrof(38km), Gareloi(55km), Kanaga(57km), Moffett(86km)
Earthquakes:
186
12 swarms found nearby.
2006
PS20060708.1(113.1km)
8 Jul
9 hours
10 earthquakes
2008
S20080502.3(10.2km)
2 May
10 days 5 hours
184 earthquakes
2017
23 Jan
2 days 23 hours
126 earthquakes
2020
S20200122.2(13.2km)
22 Jan
10 days 13 hours
627 earthquakes
2021
S20210224.2(11.2km)
23 Feb
1 day 16 hours
34 earthquakes
2022
13 Nov
1 day 7 hours
42 earthquakes
17 Nov
7 days 23 hours
341 earthquakes
2023
10 Feb
2 days 6 hours
71 earthquakes
17 Feb
6 days 13 hours
309 earthquakes
28 Feb
1 day 15 hours
114 earthquakes
4 Mar
57 days 17 hours
4231 earthquakes
22 Jun
4 days 21 hours
90 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm VS20221213.1: Analysis of Activity West of Adak, Alaska

A seismic swarm designated VS20221213.1 was recorded 92 km west of Adak, Alaska, in the Aleutian Islands. The sequence began at 12:34 on 12 December 2022 and concluded at 23:45 on 22 December 2022, spanning 251 hours and 10 minutes. During this interval, 186 earthquakes were registered.

The Aleutian Islands lie along the convergent boundary where the Pacific Plate subducts beneath the North American Plate at rates of approximately 6–8 cm per year. This tectonic setting produces frequent seismic activity and volcanic arcs. Adak Island itself sits within a region of elevated seismicity characterized by both shallow crustal events and deeper Wadati-Benioff zone earthquakes. The December 2022 swarm occurred at shallow depths, consistent with upper-plate or interface processes near the subduction zone.

Analysis of the first 100 events reveals a typical swarm signature: low-to-moderate magnitudes accompanied by tightly clustered occurrence times. Recorded magnitudes ranged from 0.0 to 2.4, with the majority falling between 0.5 and 1.5. Depths were predominantly shallow, concentrated between 0 and 7 km; many events were assigned a nominal depth of –1 km, indicating very shallow or near-surface sources. Peak activity occurred on 15 December, when multiple events above magnitude 1.5 were detected within hours, including a magnitude 2.4 shock at 2 km depth. The temporal distribution showed an initial burst on 12 December followed by sustained but declining rates through 19 December.

Historical records maintained by SeismoSight indicate that seven swarms have occurred in the same region since 1 January 2000. Prior swarms were documented in 2006, 2008, 2017, 2020, 2021, and twice in 2022. This pattern underscores the recurrent nature of swarm-type seismicity west of Adak, likely driven by episodic fluid migration or slow-slip processes along the subduction interface.

No events in the present swarm exceeded magnitude 2.5, and the sequence exhibited the classic characteristics of swarm behavior: absence of a single dominant mainshock and gradual decay in event rate. Such activity is common in the central Aleutians and rarely leads to larger triggered earthquakes, although it provides valuable data for refining local velocity models and stress-field estimates.

Continued monitoring by regional seismic networks remains essential for distinguishing swarm activity from potential foreshock sequences in this tectonically active corridor.

References

SeismoSight internal swarm catalog VS20221213.1
USGS Earthquake Hazards Program – Aleutian subduction zone reports
Alaska Earthquake Center regional seismicity summaries