Seismic Swarm VS20170129.1 Near Aleneva, Alaska: Characteristics and Regional Context

On 29 January 2017 at 06:17 UTC, a seismic swarm designated VS20170129.1 began approximately 89 km NNW of Aleneva, Alaska. The sequence concluded at 04:53 on 30 January 2017, spanning 22 hours and 36 minutes. During this period, 26 earthquakes were recorded, with magnitudes ranging from 1.2 to 2.3 and focal depths between 0 and 12 km. The largest event reached magnitude 2.3 at 08:52 on 29 January.

The swarm exhibited a typical pattern of clustered, low-magnitude activity without a dominant mainshock. Events occurred in two primary phases: an initial burst between 06:17 and 10:36 on 29 January, followed by renewed activity from 14:18 onward. Depths remained consistently shallow, indicating occurrence within the upper crust. No events exceeded magnitude 2.3, and the sequence terminated abruptly after the final recorded shock at magnitude 1.5 on 30 January.

This swarm represents the third documented episode in the area since 2000. Earlier swarms occurred in 2013 (one event) and 2016 (one event), suggesting episodic rather than continuous microseismicity. Such sequences often reflect fluid migration or minor stress adjustments along pre-existing faults within the overriding plate.

The region lies along the convergent margin where the Pacific Plate subducts beneath the North American Plate at the Alaska-Aleutian subduction zone. This tectonic setting produces frequent earthquakes, including great megathrust events. Shallow crustal seismicity, such as the 2017 swarm, commonly occurs above the plate interface in response to regional compression and local faulting. Historical records document the 1964 magnitude 9.2 Great Alaska Earthquake, whose rupture extended across the Kodiak region and produced widespread deformation. Post-1964 aftershock patterns and modern instrumental data confirm ongoing strain accumulation and release along the margin.

Aleneva and surrounding islands occupy a zone of transitional tectonics between the locked subduction interface to the east and more complex strike-slip features near the Kenai Peninsula. Shallow events at depths under 12 km align with known crustal fault systems mapped in the area. Updated monitoring by the Alaska Earthquake Center indicates that background seismicity remains elevated compared with stable continental interiors, consistent with the swarm statistics observed since 2000.

References
Alaska Earthquake Center, University of Alaska Fairbanks – Regional seismicity reports.
U.S. Geological Survey Earthquake Hazards Program – Tectonic framework of southern Alaska.
SeismoSight internal classification records for swarm VS20170129.1.