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Location:
39 km NE of Adak, Alaska
Period:
30 Jun 2018 05:12:17 - 2 Jul 2018 03:12:54 (1 day 22 hours)
Volcanoes in 100km radius:
Great Sitkin(3km), Moffett(41km), Kasatochi(46km), Kanaga(70km), Koniuji(72km), Bobrof(88km)
Earthquakes:
35
34 swarms found nearby.
2002
S20020318.1(14.6km)
17 Mar
2 days 8 hours
75 earthquakes
2013
PS20130831.1(104.3km)
31 Aug
15 hours
5 earthquakes
2018
18 Jan
2 days 7 hours
87 earthquakes
5 Jun
8 days 3 hours
430 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
14 Nov
9 days 8 hours
275 earthquakes
26 Nov
6 days 7 hours
191 earthquakes
3 Dec
7 days 18 hours
179 earthquakes
VS20181221.1(12.3km)
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
S20230102.2(10.3km)
2 Jan
23 hours
30 earthquakes
2025
PS20250320.1(104.9km)
19 Mar
22 hours
5 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm VS20180630.1: Analysis of Earthquake Activity Near Adak, Alaska

A seismic swarm designated VS20180630.1 was recorded 39 km northeast of Adak, Alaska. The sequence began at 05:12 UTC on 30 June 2018 and concluded at 03:12 UTC on 2 July 2018, spanning 46 hours and encompassing 35 earthquakes. All events exhibited very low magnitudes, ranging from -0.8 to 0.1, with focal depths predominantly between -1 km and 3 km. These characteristics align with typical swarm behavior in tectonically active subduction zones, where clustered microseismicity often reflects fluid migration or stress adjustments along fault networks without a dominant mainshock.

The Adak region lies within the central Aleutian Islands, part of the Pacific Ring of Fire. This area experiences intense seismic and volcanic activity due to the oblique subduction of the Pacific Plate beneath the North American Plate along the Aleutian Trench. Convergence rates average approximately 6–7 cm per year, driving megathrust earthquakes and frequent aftershock sequences. The local geology features a complex arrangement of volcanic arcs, accreted terranes, and active fault systems, including the Adak Island volcanic complex. Historical records indicate that the central Aleutians have hosted multiple magnitude 7+ events in the past century, underscoring the persistent tectonic strain accumulation.

Earthquake swarms have occurred intermittently in this sector since systematic monitoring began. Since 1 January 2000, four distinct swarms have been identified in the vicinity: one in 2002, one in 2013, and two in 2018. The 2018 pair, including VS20180630.1, represents the most recent cluster. Such swarms are not uncommon in the Aleutians and may relate to transient processes such as magma movement or hydrothermal fluid circulation within the overriding plate, though they rarely escalate to damaging earthquakes.

The temporal distribution of the VS20180630.1 events shows an initial peak of activity on 30 June, followed by a gradual decline through 1 July and a final event early on 2 July. Magnitudes remained consistently below 0.1, indicating a diffuse release of strain rather than a classic foreshock-mainshock-aftershock pattern. Depths clustered near the surface suggest involvement of shallow crustal structures, consistent with regional volcanic and tectonic interactions.

Ongoing monitoring by regional seismic networks continues to track background seismicity in the central Aleutians. The low-energy nature of VS20180630.1 poses no significant hazard to nearby communities on Adak Island, yet it contributes valuable data for refining models of subduction-zone dynamics.

References

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