Location:

Period:

16 Jul 2011 19:59:12 - 19 Jul 2011 13:02:49 (2 days 17 hours 3 minutes)

Volcanoes in 100km radius:

Dutton(91km), Emmons Lake Volcanic Center(94km), Pavlof(94km), Pavlof Sister(97km)

Earthquakes:

6 swarms found nearby.

2007

PS20071002.1(45.6km)

2 Oct

2 hours

5 earthquakes

2020

S20200728.1(6.5km)

27 Jul

5 days 4 hours

111 earthquakes

S20200805.1(20.9km)

4 Aug

1 day 16 hours

45 earthquakes

S20200809.1(2.8km)

8 Aug

3 days 18 hours

43 earthquakes

PS20201019.2(103.9km)

19 Oct

1 day 4 hours

12 earthquakes

2023

S20230716.3(6.8km)

16 Jul

6 days 3 hours

65 earthquakes

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Earthquake Swarm S20110717.1: Seismic Insights Near Sand Point, Alaska

The earthquake swarm designated S20110717.1 occurred 77 km south-southwest of Sand Point, Alaska, within the tectonically active Aleutian subduction zone. This region lies where the Pacific Plate subducts beneath the North American Plate, generating frequent seismic events due to plate convergence at rates of approximately 6–7 cm per year. The swarm initiated at 19:59 on 16 July 2011 and concluded at 13:02 on 19 July 2011, spanning 65 hours and 3 minutes during which 34 earthquakes were recorded.

The sequence began with a magnitude 6.1 event at 36 km depth. Subsequent activity included a magnitude 3.1 shock at 13 km depth shortly afterward, followed by numerous smaller events clustered primarily between 13 km and 25 km depth. Notable later events comprised magnitudes of 2.9 at 6 km, 3.0 at 10 km, 2.7 at 25 km, 2.7 at 13 km, and 3.0 at 14 km. The majority of events registered below magnitude 2.5, with depths predominantly in the 13–25 km range, consistent with crustal stresses in the overriding plate and interface.

This swarm reflects episodic stress adjustment along the subduction interface and overlying crust, a common process in the Aleutian arc. Depths indicate activity both near the plate boundary and within the North American Plate. Such swarms provide data on fault segmentation and fluid migration influences in the forearc environment.

Geologically, the Sand Point vicinity forms part of the Alaska Peninsula's volcanic arc, shaped by millions of years of subduction. Historical records show recurrent moderate-to-large earthquakes, with the prior classified swarm in this locale occurring in 2007. Since 1 January 2000, this event marks the second swarm documented under internal classification protocols.

The 2011 activity underscores the persistent seismic hazard in this remote stretch of the Aleutian system, where monitoring supports regional hazard assessment and tectonic research.

References
SeismoSight internal swarm classification database
USGS Earthquake Catalog
Alaska Earthquake Center regional reports