Location:

Period:

2 Nov 2024 14:15:41 - 4 Nov 2024 05:12:29 (1 day 14 hours 56 minutes)

Volcanoes in 100km radius:

Great Sitkin(81km), Kasatochi(84km), Koniuji(94km), Moffett(97km)

Earthquakes:

9 swarms found nearby.

2008

PS20081031.1(85.5km)

31 Oct

1 day 9 hours

6 earthquakes

2010

S20100903.1(26.1km)

3 Sep

3 days 1 hours

49 earthquakes

2013

PS20130831.1(46.7km)

31 Aug

15 hours

5 earthquakes

PS20130904.2(72.6km)

4 Sep

1 day 7 hours

11 earthquakes

2015

PS20150905.1(87.7km)

4 Sep

18 hours

5 earthquakes

2016

PS20160319.1(107.4km)

18 Mar

15 hours

5 earthquakes

2017

PS20170509.1(103.0km)

8 May

17 hours

5 earthquakes

2019

S20191124.1(9.6km)

24 Nov

2 days 4 hours

84 earthquakes

2025

PS20250320.1(48.6km)

19 Mar

22 hours

5 earthquakes

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Seismic Swarm S20241103.1: Analysis of Recent Activity Southeast of Adak, Alaska

A seismic swarm designated S20241103.1 was recorded southeast of Adak in the Aleutian Islands, Alaska. The sequence began at 14:15 on 2 November 2024 and concluded at 05:12 on 4 November 2024, spanning 38 hours and 56 minutes. During this period, 52 earthquakes were registered at a location approximately 79 km southeast of Adak.

The swarm featured a range of magnitudes, with the largest event reaching 5.8 on 3 November at 10:56:48 UTC at a depth of 34 km. Subsequent notable events included a 4.1 magnitude earthquake minutes later at 35 km depth, followed by a 3.8 magnitude shock at 11:28:22 and a 3.4 magnitude event at 21:16:44, both near 35 km depth. Smaller events, predominantly between 1.5 and 2.8 in magnitude, clustered at depths of 15–35 km, with occasional shallower occurrences around 4 km. The sequence tapered with a final 3.2 magnitude event at 05:12 on 4 November at 35 km depth.

This activity occurred within the tectonically active 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. The region experiences frequent seismicity due to this megathrust interface, which extends along the island arc and has produced some of the largest earthquakes in U.S. history, including the 1957 Andreanof Islands event of magnitude 8.6. Depths in the 20–45 km range align with typical intermediate-depth activity along the subducting slab.

Historical records indicate that swarm-type sequences are recurrent in this sector of the Aleutians. Since 2000, eight such swarms have been documented in the vicinity, occurring in 2008, 2010, 2013 (two instances), 2015, 2016, 2017, and 2019. These episodes generally reflect episodic stress release along the subduction interface or associated crustal faults rather than precursory signals to larger mainshock-aftershock sequences.

The S20241103.1 swarm exemplifies the clustered, moderate-magnitude character common to Aleutian seismicity, with events distributed across a compact time window and focal depths consistent with slab-related processes. No damage or tsunami impacts were associated with the activity.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Alaska Earthquake Center regional reports
SeismoSight internal swarm classification data