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Location:
39 km ENE of Adak, Alaska
Period:
14 Nov 2018 11:07:31 - 23 Nov 2018 19:45:50 (9 days 8 hours 38 minutes)
Volcanoes in 100km radius:
Great Sitkin(1km), Kasatochi(44km), Moffett(44km), Koniuji(70km), Kanaga(73km), Bobrof(91km)
Earthquakes:
275
34 swarms found nearby.
2002
S20020318.1(17.3km)
17 Mar
2 days 8 hours
75 earthquakes
2013
PS20130831.1(102.8km)
31 Aug
15 hours
5 earthquakes
2018
18 Jan
2 days 7 hours
87 earthquakes
5 Jun
8 days 3 hours
430 earthquakes
30 Jun
1 day 22 hours
35 earthquakes
8 Sep
3 days 3 hours
52 earthquakes
28 Sep
1 day 22 hours
33 earthquakes
27 Oct
7 days 6 hours
253 earthquakes
26 Nov
6 days 7 hours
191 earthquakes
3 Dec
7 days 18 hours
179 earthquakes
20 Dec
2 days 1 hours
30 earthquakes
2019
17 Jun
3 days 10 hours
80 earthquakes
6 Oct
3 hours
37 earthquakes
2020
18 Jan
5 days 5 hours
119 earthquakes
29 Jan
2 days 14 hours
72 earthquakes
2 Feb
1 day 14 hours
37 earthquakes
6 Feb
6 days 21 hours
144 earthquakes
25 Feb
20 days 20 hours
580 earthquakes
20 Mar
31 days 4 hours
579 earthquakes
23 Apr
15 days 9 hours
279 earthquakes
14 May
5 days 18 hours
76 earthquakes
30 May
10 days 21 hours
210 earthquakes
14 Jun
4 days 1 hours
69 earthquakes
5 Jul
11 days 1 hours
252 earthquakes
18 Jul
3 days 5 hours
57 earthquakes
7 Nov
1 day 14 hours
31 earthquakes
2021
25 May
1 day 3 hours
165 earthquakes
22 Jun
2 days 8 hours
34 earthquakes
11 Jul
5 days 5 hours
120 earthquakes
23 Jul
5 days 4 hours
83 earthquakes
28 Jul
8 days 13 hours
161 earthquakes
11 Aug
2 days 19 hours
49 earthquakes
2023
2 Jan
23 hours
30 earthquakes
2025
PS20250320.1(105.7km)
19 Mar
22 hours
5 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm VS20181115.1: Analysis of Activity Near Adak, Alaska

A seismic swarm designated VS20181115.1 was recorded 39 km east-northeast of Adak, Alaska. The sequence began at 11:07 on 14 November 2018 and concluded at 19:45 on 23 November 2018, spanning 224 hours and 38 minutes. During this interval, 275 earthquakes were registered. The first 100 events displayed predominantly low magnitudes, ranging from -1.0 to 1.2. Depths were mostly shallow, between -1 km and 5 km, with isolated deeper occurrences at 21 km and 30 km. Early activity on 14 November included events at magnitudes 0.0 to 0.8, followed by clusters of negative-magnitude tremors on 15 and 16 November. Notable peaks reached 1.2 on 15 November at 14:36 and 1.1 on 15 November at 10:15 and 12:04. The pattern indicates a typical swarm progression of numerous small events without a single dominant mainshock. Adak lies within the Aleutian Islands arc, a tectonically active segment of the Pacific Ring of Fire. The region experiences intense seismicity due to subduction of the Pacific Plate beneath the North American Plate at rates of approximately 6–8 cm per year. This convergence produces both shallow crustal earthquakes and deeper Wadati-Benioff zone activity, alongside frequent volcanism. The Andreanof Islands sector, where the swarm occurred, has hosted several magnitude 7+ events historically, reflecting the high strain accumulation along the megathrust. Earthquake swarms have occurred in the Adak vicinity since at least 2000, with eight documented episodes. Prior swarms took place in 2002 (one swarm) and 2013 (one swarm), while six occurred in 2018. These sequences typically feature low-magnitude events at shallow depths, consistent with fluid migration or stress triggering within the overriding plate or along the subduction interface. The VS20181115.1 swarm aligns with this regional pattern, contributing to ongoing monitoring of seismic hazards in the central Aleutians. Continued observation supports improved understanding of precursory activity ahead of larger tectonic events.

References

USGS Earthquake Hazards Program – Aleutian Islands seismicity reports
Alaska Earthquake Center – Regional tectonic summaries
SeismoSight internal swarm classification records