Location:

Period:

5 Oct 2024 12:50:24 - 7 Oct 2024 12:31:09 (1 day 23 hours 40 minutes)

Volcanoes in 100km radius:

Okmok(82km), Makushin(83km)

Earthquakes:

3 swarms found nearby.

2009

PS20091013.1(61.7km)

13 Oct

14 hours

5 earthquakes

2022

PS20220111.1(85.0km)

11 Jan

3 hours

8 earthquakes

S20220122.1(20.0km)

22 Jan

3 days 22 hours

78 earthquakes

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Earthquake Swarm S20241006.1: Seismic Activity Near Unalaska, Alaska

An earthquake swarm designated S20241006.1 occurred approximately 78 km south-southwest of Unalaska in the Aleutian Islands, Alaska. The sequence began at 12:50 UTC on 5 October 2024 and concluded at 12:31 UTC on 7 October 2024, spanning 47 hours and 40 minutes. During this period, 28 earthquakes were recorded, with magnitudes ranging from 1.8 to 5.4 and focal depths between 12 km and 55 km.

The swarm initiated with two closely spaced events: a magnitude 4.6 quake at 46 km depth, followed within seconds by the largest event of magnitude 5.4 at 41 km depth. Subsequent activity included multiple events above magnitude 4.0, notably a magnitude 4.4 at 50 km depth later on 5 October, a magnitude 4.1 at 49 km on 6 October, a magnitude 4.2 at 35 km, and peaks of magnitude 4.8 at 55 km and 4.5 at 52 km. Shallower events clustered around 25–35 km depth, with the sequence tapering to smaller magnitudes by 7 October.

The Aleutian Islands lie along the convergent boundary where the Pacific Plate subducts beneath the North American Plate at rates of approximately 6–7 cm per year. This tectonic setting produces intense seismicity, including both interplate thrust earthquakes and intraslab events within the downgoing slab. Unalaska and surrounding islands experience frequent earthquake swarms due to fluid migration, stress transfer, and volcanic processes associated with the Aleutian arc. Depths in the 20–55 km range align with typical intraslab seismicity in this subduction zone.

Historically, the region has recorded multiple swarms since 2000. Only three prior swarms have been identified: one in 2009 and two in 2022. These episodes reflect episodic release of accumulated strain without progression to a mainshock-aftershock sequence.

No significant damage or tsunami generation was associated with Swarm S20241006.1, consistent with its moderate magnitudes and offshore location. Continued monitoring by regional seismic networks remains essential given the area's elevated seismic hazard.

References

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