Location:

Period:

9 Sep 2019 03:54:06 - 10 Sep 2019 23:15:54 (1 day 19 hours 21 minutes)

Volcanoes in 100km radius:

Gareloi(41km), Tanaga(62km), Takawangha(67km)

Earthquakes:

112

8 swarms found nearby.

2006

PS20060708.1(46.7km)

8 Jul

9 hours

10 earthquakes

PS20060826.1(56.9km)

26 Aug

47 minutes

6 earthquakes

2007

PS20071219.1(50.6km)

19 Dec

19 hours

12 earthquakes

2013

S20130121.1(29.1km)

21 Jan

3 days 11 hours

62 earthquakes

S20131113.2(11.9km)

13 Nov

3 days 20 hours

78 earthquakes

2017

S20170508.1(22.7km)

7 May

3 days 10 hours

165 earthquakes

2020

PS20200126.1(91.4km)

26 Jan

18 hours

8 earthquakes

2023

S20230613.1(17.2km)

13 Jun

1 day 7 hours

40 earthquakes

AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20190909.1: Earthquake Activity West of Adak, Alaska

Seismic swarm S20190909.1 was recorded 151 km west-southwest of Adak, Alaska, in the central Aleutian Islands. The sequence began at 03:54 UTC on 9 September 2019 and concluded at 23:15 UTC on 10 September 2019, spanning 43 hours and 21 minutes. During this interval, 112 earthquakes were detected.

The Aleutian Islands form part of an active subduction zone where the Pacific Plate descends beneath the North American Plate at rates of approximately 6–7 cm per year. This tectonic setting produces frequent seismic activity, including both individual large-magnitude events and episodic swarms. The swarm location lies along the arc’s volcanic front, where crustal stresses associated with plate convergence commonly generate shallow to intermediate-depth earthquakes.

Analysis of the first 100 events shows magnitudes ranging from 1.0 to 5.4. The largest event, magnitude 5.4, occurred at 16 km depth at the swarm’s onset. Subsequent events clustered between 7 km and 18 km depth, with the majority between 8 km and 14 km. Magnitudes declined rapidly after the initial shock, with most events below magnitude 2.0. A secondary peak included a magnitude 3.9 event at 10 km depth roughly two hours after the start. Depths remained consistent within the upper crust, consistent with typical Aleutian swarm patterns driven by fluid migration or stress transfer along local fault networks.

Historical records indicate six prior swarms in the same region since 1 January 2000. These occurred in 2006 (two swarms), 2007 (one swarm), 2013 (two swarms), and 2017 (one swarm). Such recurrent swarms reflect ongoing tectonic loading within the subduction interface and overlying crust.

The 2019 swarm’s temporal evolution—rapid onset followed by a decaying rate of smaller events—aligns with patterns observed in other subduction-related swarms worldwide. No damage or felt reports were associated with the sequence, reflecting both the offshore location and modest magnitudes after the initial event.

References
SeismoSight internal swarm classification S20190909.1
USGS Earthquake Hazards Program – Aleutian Arc tectonics overview
Alaska Earthquake Center – regional seismicity summaries