Location:

Period:

17 May 2023 14:59:01 - 20 May 2023 09:01:17 (2 days 18 hours 2 minutes)

Volcanoes in 100km radius:

Mageik(1km), Martin(5km), Novarupta(9km), Trident(11km), Griggs(20km), Katmai(20km), Unnamed(37km), Snowy Mountain(37km), Denison(54km), Steller(57km), Kukak(60km), Ugashik-Peulik(81km), Ukinrek Maars(83km), Kaguyak(86km)

Earthquakes:

15 swarms found nearby.

2019

VS20190905.1(13.4km)

4 Sep

23 days 3 hours

423 earthquakes

2020

S20200126.1(27.9km)

25 Jan

3 days 12 hours

54 earthquakes

VS20200403.1(3.8km)

2 Apr

4 days 11 hours

61 earthquakes

2022

VS20220825.1(21.5km)

24 Aug

4 days 10 hours

146 earthquakes

VS20220902.1(5.4km)

1 Sep

6 days 9 hours

108 earthquakes

VS20220922.1(11.2km)

21 Sep

1 day 4 hours

54 earthquakes

VS20221112.1(2.4km)

11 Nov

73 days 1 hours

1277 earthquakes

2023

VS20230127.1(1.5km)

26 Jan

109 days 4 hours

2489 earthquakes

VS20230331.1(23.3km)

30 Mar

1 day 12 hours

25 earthquakes

VS20230524.1(4.3km)

23 May

98 days 12 hours

3637 earthquakes

VS20230903.1(2.4km)

2 Sep

14 days 6 hours

242 earthquakes

VS20230923.1(3.8km)

22 Sep

8 days 4 hours

121 earthquakes

VS20231022.1(12.8km)

21 Oct

6 days 8 hours

82 earthquakes

2024

VS20240524.1(16.9km)

24 May

1 day 0 hours

32 earthquakes

2026

S20260515.1(19.1km)

15 May

20 hours

39 earthquakes

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Seismic Swarm VS20230518.1: Analysis of Activity Near Karluk, Alaska

A seismic swarm designated VS20230518.1 occurred approximately 85 km NNW of Karluk, Alaska, on Kodiak Island. The sequence began at 14:59 on 17 May 2023 and concluded at 09:01 on 20 May 2023, spanning 66 hours and 2 minutes. During this period, 45 earthquakes were recorded, with magnitudes ranging from -0.6 to 1.9 and focal depths predominantly between 0 and 7 km, though a few events reached depths of 28–34 km.

The swarm exhibited a typical pattern of clustered microseismicity without a dominant mainshock. Initial events on 17 May included magnitudes of 1.3 and 1.1 at shallow depths of 3 km and 1 km. Activity intensified on 18 May, featuring multiple events around magnitude 1.0–1.9 clustered between 03:00 and 13:00 UTC, followed by a gradual decline through 19 and 20 May. Depths remained mostly crustal, consistent with shallow tectonic processes in the overriding plate.

This region lies within the tectonically active Aleutian subduction zone, where the Pacific Plate converges with the North American Plate at rates of approximately 6–7 cm per year. Kodiak Island experiences frequent seismicity due to megathrust locking and episodic slip along the plate interface, as well as upper-plate faulting. Historical records document numerous earthquake swarms in the broader Kodiak area since 2000, with nine such sequences identified through 2023. Prior swarms occurred in 2019 (one event), 2020 (two events), 2022 (four events), and 2023 (two events, including the present sequence).

Seismic swarms in subduction settings often reflect fluid migration, stress transfer, or aseismic slip transients rather than volcanic processes. The shallow depths and low magnitudes observed here align with background tectonic strain release along secondary faults. No significant damage or felt reports were associated with this swarm, reflecting the microseismic character of the events.

Long-term monitoring by regional networks continues to track such sequences to refine models of plate-boundary behavior. The 1964 Great Alaska Earthquake (Mw 9.2) demonstrated the potential for much larger events in this zone, underscoring the importance of ongoing surveillance.

References

Alaska Earthquake Center, University of Alaska Fairbanks
USGS Earthquake Catalog and Tectonic Summaries
SeismoSight internal swarm classification records