Location:

Period:

19 Mar 2025 18:50:30 - 25 Mar 2025 23:51:48 (6 days 5 hours 1 minute)

Volcanoes in 100km radius:

None

Earthquakes:

182

7 swarms found nearby.

2010

S20101104.2(26.0km)

3 Nov

4 days 9 hours

177 earthquakes

S20101220.1(4.8km)

19 Dec

2 days 18 hours

48 earthquakes

S20101226.1(1.4km)

25 Dec

3 days 20 hours

102 earthquakes

2013

PS20130831.1(95.5km)

31 Aug

15 hours

5 earthquakes

2017

PS20170509.1(57.7km)

8 May

17 hours

5 earthquakes

2020

S20200511.1(20.9km)

11 May

1 day 3 hours

32 earthquakes

2025

PS20250320.1(10.6km)

19 Mar

22 hours

5 earthquakes

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Seismic Swarm S20250320.1 Near Adak, Alaska

A seismic swarm designated S20250320.1 occurred 97 km south-southeast of Adak, Alaska, in the central Aleutian Islands. The sequence began at 18:50 UTC on 19 March 2025 and concluded at 23:51 UTC on 25 March 2025, spanning 149 hours and registering 182 earthquakes.

The swarm unfolded within the Aleutian subduction zone, where the Pacific Plate converges with and subducts beneath the North American Plate at rates of approximately 6–7 cm per year. This tectonic setting produces the region’s elevated seismicity and volcanic activity along the Aleutian Arc. Earthquakes in this area commonly occur at depths of 10–40 km, consistent with the observed swarm depths that ranged primarily between 10 km and 35 km.

Analysis of the first 100 events reveals a typical swarm pattern of clustered, moderate-magnitude activity without a single dominant mainshock. Magnitudes varied from 2.1 to 6.2, with the largest event (M6.2) recorded at 17 km depth on 21 March 2025 at 14:53 UTC. Additional notable shocks included an M5.9 at 26 km depth shortly afterward and several M4.0–M4.9 events distributed throughout the sequence. Depths showed a bimodal distribution, with many events at 10 km and others near 35 km, reflecting activity along both shallower crustal faults and the deeper plate interface.

Historical records indicate that seven comparable swarms have occurred in the same sector since 2000. Prior episodes took place in 2010 (three swarms), 2013 (one), 2017 (one), 2020 (one), and 2025 (one). These recurrent swarms underscore the persistent stress accumulation and release characteristic of the central Aleutians.

The March 2025 sequence remained within expected parameters for background seismicity in this highly active subduction environment. No significant damage or tsunami generation was associated with the events, consistent with their moderate magnitudes and offshore location.

References

Alaska Earthquake Center, University of Alaska Fairbanks
U.S. Geological Survey Earthquake Hazards Program
SeismoSight internal swarm classification database