Location:

Period:

17 Jul 2010 14:15:16 - 12 Sep 2010 07:01:40 (56 days 16 hours 46 minutes)

Volcanoes in 100km radius:

Tana(41km), Kagamil(50km), Cleveland(51km), Herbert(58km), Uliaga(60km), Carlisle(61km), Vsevidof(70km), Recheschnoi(78km), Yunaska(91km)

Earthquakes:

2676

12 swarms found nearby.

2007

PS20071227.1(74.0km)

26 Dec

17 hours

7 earthquakes

2010

S20100718.3(17.9km)

17 Jul

21 days 2 hours

625 earthquakes

S20100719.1(17.5km)

18 Jul

17 days 10 hours

390 earthquakes

S20100812.1(20.1km)

11 Aug

1 day 22 hours

41 earthquakes

S20100815.1(13.8km)

14 Aug

1 day 7 hours

34 earthquakes

S20101112.2(17.8km)

11 Nov

2 days 5 hours

44 earthquakes

2014

S20140802.1(12.8km)

1 Aug

3 days 5 hours

36 earthquakes

S20140813.1(18.1km)

12 Aug

2 days 14 hours

53 earthquakes

S20140819.2(24.0km)

18 Aug

1 day 12 hours

43 earthquakes

2015

PS20150727.1(32.5km)

27 Jul

3 hours

8 earthquakes

2017

S20170810.1(28.5km)

9 Aug

2 days 7 hours

32 earthquakes

2022

PS20220111.1(83.0km)

11 Jan

3 hours

8 earthquakes

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

Seismic Swarm S20100718.1: Analysis of Activity Southwest of Nikolski, Alaska

The seismic swarm designated S20100718.1 occurred in a tectonically active segment of the Aleutian Islands, approximately 40 km southwest of Nikolski, Alaska. Registration began at 14:15 on 17 July 2010 and concluded at 07:01 on 12 September 2010, spanning 1360 hours and 46 minutes. During this interval, 2676 earthquakes were recorded, consistent with internal SeismoSight classification protocols that treat swarm parameters as given without external verification.

Analysis of the first 100 events reveals a rapid escalation in activity following the initial M2.1 shock. Early events remained modest, with magnitudes between 1.9 and 2.0 at depths of 4–6 km. Within hours, a pronounced cluster developed on 18 July between 06:02 and 07:52, featuring multiple events exceeding magnitude 3.5. Notable shocks included M3.9 at 06:13:51 (15 km depth), M4.5 at 06:15:48 (4 km), M4.7 at 06:16:37 (6 km), and M4.2 at 07:52:02 (3 km). Depths for these initial events were predominantly shallow, ranging from 1 km to 15 km, with one deeper outlier of M4.3 recorded at 35 km on 18 July at 09:07:30. Subsequent events through 19 July maintained magnitudes mostly between 2.1 and 3.4, illustrating a classic swarm pattern of numerous small-to-moderate quakes without a single dominant mainshock.

The Aleutian arc forms part of the circum-Pacific seismic belt, where the Pacific Plate subducts northwestward beneath the North American Plate at rates of approximately 6–7 cm per year. This convergent margin generates frequent seismicity and volcanism along the island chain. Nikolski lies on Umnak Island, near the intersection of the subduction interface and regional fault systems that accommodate both thrust and strike-slip motion. Historical records document recurrent earthquake swarms in the central Aleutians, reflecting episodic stress release along the megathrust and overlying crustal structures. The 2010 swarm aligns with this regional behavior, occurring in a zone previously active during a comparable episode in 2007—the sole prior swarm noted in records since 1 January 2000.

Shallow focal depths observed in the early events suggest involvement of the overriding plate and possibly fluid migration or magmatic processes associated with nearby volcanic centers such as Okmok Caldera. Such swarms can precede or accompany volcanic unrest, although no eruptive activity was linked to this sequence. The overall duration and event count underscore the capacity of subduction-related crust to sustain prolonged microseismic episodes.

USGS Earthquake Hazards Program regional tectonic summaries
Alaska Volcano Observatory geological framework reports
SeismoSight internal swarm classification records