Seismic Analysis of Swarm VS20221112.1 Near Karluk, Alaska
The Kodiak Island region of Alaska lies within the tectonically active Alaska-Aleutian subduction zone, where the Pacific Plate converges with and subducts beneath the North American Plate at rates exceeding 6 cm per year. This setting produces frequent earthquakes, volcanic activity, and associated seismic swarms. The area approximately 84 km north-northwest of Karluk experiences elevated seismicity due to its position along the megathrust interface and overlying crustal faults.
Swarm VS20221112.1 was recorded from 20:03 on 11 November 2022 until 21:07 on 23 January 2023, encompassing 1,753 hours and 4 minutes. A total of 1,277 earthquakes were detected during this interval. The events clustered at shallow depths, consistent with activity in the upper crust above the subduction interface.
Examination of the first 100 events reveals predominantly microseismic activity. Magnitudes ranged from -0.9 to 1.9, with the majority falling between -0.5 and 0.8. Depths typically varied between 0 and 7 km, indicating shallow crustal sources. Notable early events included a magnitude 1.9 earthquake at 3 km depth on 14 November 2022 and a magnitude 1.6 event at 0 km depth later the same day. Negative magnitudes reflect the high sensitivity of the monitoring network to very small events. Temporal distribution showed initial clustering within the first 48 hours, followed by sporadic occurrences through mid-November.
Historical records since 1 January 2000 document nine comparable swarms in the region. Earlier episodes occurred in 2002 (one swarm), 2019 (two swarms), 2020 (three swarms), and 2022 (three swarms). These recurrent swarms underscore the persistent stress accumulation and release along local fault structures influenced by ongoing plate subduction.
The shallow depth distribution and low-magnitude character of VS20221112.1 align with patterns observed in prior swarms, suggesting fluid migration or aseismic slip as possible driving mechanisms within the overriding plate. Continued monitoring remains essential for assessing any evolution toward larger events in this high-hazard zone.
References
SeismoSight internal swarm classification records
USGS Earthquake Catalog (Alaska region, 2000–2023)
Alaska Earthquake Center regional tectonic summaries