Seismic Swarm S20130830.2 Near Atka, Alaska: Geological Context and Event Analysis

A seismic swarm designated S20130830.2 occurred 104 km south-southwest of Atka, Alaska, in the central Aleutian Islands. The sequence began at 16:33 UTC on 30 August 2013 and concluded at 14:42 UTC on 1 September 2013, lasting 46 hours and 9 minutes. During this interval, 198 earthquakes were recorded. The Aleutian Islands lie within the circum-Pacific Ring of Fire, where the Pacific Plate subducts beneath the North American Plate along the Aleutian Trench. This tectonic setting produces frequent earthquakes and active volcanism, including nearby volcanoes such as Korovin and Kliuchef on Atka Island. Earthquake depths in the region commonly range from shallow crustal levels to approximately 30 km, consistent with the observed swarm activity. Analysis of the first 100 events reveals a broad magnitude range from 1.4 to 6.0, with the majority falling between 2.0 and 4.0. Depths varied from 0 km to 33 km, indicating both shallow and intermediate-depth sources. Notable larger events included a magnitude 6.0 earthquake at 18 km depth on 31 August at 06:38:36 UTC, a magnitude 5.2 at 10 km on the same day, and several magnitude 4.8–4.9 shocks clustered between 06:31 and 07:04 UTC. The sequence exhibited typical swarm characteristics: rapid onset, lack of a single dominant mainshock, and gradual decay in event rate. Historical records indicate that three swarms have occurred in the immediate region since 1 January 2000. Prior episodes took place in 2008 (one swarm) and 2010 (one swarm), underscoring the recurrent nature of clustered seismicity along this segment of the subduction zone. The 2013 swarm did not produce reported damage or tsunami, consistent with its offshore location and moderate maximum magnitudes. Continued monitoring by regional seismic networks remains essential for assessing potential links to volcanic unrest in the central Aleutians.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Alaska Volcano Observatory reports on Aleutian tectonics