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Note:This page contains AI-generated content for informational and entertainment purposes only. It may contain inaccuracies. Raw event data is from USGS and EMSC. All statistics, lists, and derived information are generated by this site. Full disclaimerFound an error?
Location:
87 km W of Adak, Alaska
Period:
23 Feb 2021 13:51:43 - 25 Feb 2021 06:20:30 (1 day 16 hours 28 minutes)
Volcanoes in 100km radius:
Takawangha(11km), Tanaga(21km), Bobrof(27km), Kanaga(46km), Gareloi(66km), Moffett(75km)
Earthquakes:
34
14 swarms found nearby.
2008
S20080502.1(20.8km)
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
22 Jan
10 days 13 hours
627 earthquakes
2022
VS20221114.1(10.5km)
13 Nov
1 day 7 hours
42 earthquakes
17 Nov
7 days 23 hours
341 earthquakes
VS20221213.1(11.2km)
12 Dec
10 days 11 hours
186 earthquakes
2023
VS20230211.1(11.4km)
10 Feb
2 days 6 hours
71 earthquakes
17 Feb
6 days 13 hours
309 earthquakes
28 Feb
1 day 15 hours
114 earthquakes
VS20230304.1(17.0km)
4 Mar
57 days 17 hours
4231 earthquakes
VS20230623.1(14.4km)
22 Jun
4 days 21 hours
90 earthquakes
2024
S20240416.1(26.9km)
15 Apr
1 day 16 hours
35 earthquakes
S20240419.2(26.2km)
18 Apr
12 days 8 hours
252 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20210224.2: Analysis of Activity West of Adak, Alaska

Seismic swarm S20210224.2 occurred approximately 87 km west of Adak, Alaska, in the Andreanof Islands region of the Aleutian chain. The sequence began at 13:51 on 23 February 2021 and concluded at 06:20 on 25 February 2021, spanning 40 hours and 28 minutes. During this period, 34 earthquakes were recorded, with magnitudes ranging from 0.0 to 1.5 and focal depths primarily between 3 and 8 km. The events clustered tightly in both time and space, consistent with swarm behavior rather than a typical mainshock-aftershock sequence.

The swarm initiated with a magnitude 0.3 event at 3 km depth. Subsequent activity intensified on 23 February evening and peaked on 24 February, featuring the largest event of magnitude 1.5 at 4 km depth around 11:29. Later events on 24 and 25 February remained small, with most magnitudes below 1.0 and depths stabilizing near 6–7 km. This pattern of low-magnitude, shallow seismicity suggests fluid migration or localized stress adjustments along minor faults within the overriding plate.

The Adak region lies along the Aleutian subduction zone, where the Pacific Plate converges with the North American Plate at rates of approximately 6–7 cm per year. This tectonic setting produces frequent earthquakes, including great megathrust events. Adak Island itself sits near the Andreanof Islands segment, which hosted the magnitude 8.6 earthquake in 1957 and the magnitude 7.9 event in 1996. Ongoing volcanic activity at nearby volcanoes such as Great Sitkin further contributes to the dynamic crustal environment.

Historical records indicate four prior swarms in the immediate area since 2000, occurring in 2008 (two swarms), 2017 (one swarm), and 2020 (one swarm). These episodes highlight recurrent, low-level seismic clustering that does not necessarily precede larger earthquakes but reflects the active subduction dynamics of the central Aleutians.

Overall, swarm S20210224.2 represents typical background seismicity in a highly active convergent margin, providing valuable data for monitoring crustal stress and potential volcanic interactions in the region.

References

USGS Earthquake Catalog
Alaska Earthquake Center reports
NOAA Paleotsunami Database