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Location:
92 km W of Adak, Alaska
Period:
28 Feb 2023 04:38:10 - 1 Mar 2023 19:56:26 (1 day 15 hours 18 minutes)
Volcanoes in 100km radius:
Takawangha(3km), Tanaga(13km), Bobrof(36km), Kanaga(54km), Gareloi(57km), Moffett(83km)
Earthquakes:
114
12 swarms found nearby.
2008
S20080502.1(28.3km)
2 May
19 days 15 hours
1079 earthquakes
2 May
10 days 5 hours
184 earthquakes
2017
23 Jan
2 days 23 hours
126 earthquakes
2020
S20200122.2(10.5km)
22 Jan
10 days 13 hours
627 earthquakes
2021
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
12 Dec
10 days 11 hours
186 earthquakes
2023
10 Feb
2 days 6 hours
71 earthquakes
17 Feb
6 days 13 hours
309 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 VS20230228.1: Activity Near Adak, Alaska

A seismic swarm designated VS20230228.1 was recorded 92 km west of Adak, Alaska, in the Aleutian Islands. The sequence began at 04:38 on 28 February 2023 and concluded at 19:56 on 1 March 2023, encompassing 114 earthquakes over 39 hours and 18 minutes. This event aligns with the region's established pattern of clustered seismicity driven by tectonic forces.

The Aleutian Islands lie along the convergent boundary where the Pacific Plate subducts beneath the North American Plate at rates of approximately 6–7 cm per year. This subduction zone generates frequent earthquakes and volcanic activity, forming part of the Pacific Ring of Fire. Adak itself sits on Adak Island within the Andreanof Islands group, an area marked by historical large-magnitude events, including the 1957 Andreanof Islands earthquake of magnitude 8.6. Depths of recorded events in the swarm ranged primarily from 2 to 12 km, consistent with shallow crustal adjustments above the subducting slab.

Analysis of the first 100 events reveals a predominance of low-magnitude activity. Magnitudes spanned 0.7 to 3.5, with the majority falling between 1.0 and 2.0. Notable peaks included a magnitude 3.5 event at 22:41 on 28 February at 8 km depth and a magnitude 3.4 at 22:43 at 9 km depth. Depths clustered around 3–6 km for most events, though several reached 9–12 km later in the sequence. Timing showed initial sparse occurrences followed by denser clustering between 21:00 on 28 February and 04:00 on 1 March, indicative of fluid migration or stress transfer along local faults.

Historical records since 2000 document ten prior swarms in the vicinity. These occurred in 2008 (two swarms), 2017 (one), 2020 (one), 2021 (one), 2022 (three), and 2023 (two). Such recurrent swarms underscore the ongoing tectonic loading in the central Aleutians without progression to a major mainshock in this instance.

The swarm's characteristics—short duration, modest magnitudes, and shallow depths—suggest it resulted from localized stress release rather than widespread rupture. Monitoring continues to track potential after-effects in this highly active subduction environment.

References

SeismoSight internal swarm classification VS20230228.1 data archive.
USGS Earthquake Catalog for Adak, Alaska region (2000–2023).
Alaska Earthquake Center regional tectonic summaries.