Seismic Swarm VS20241102.1: Analysis of Activity Near Beluga, Alaska

Seismic swarm VS20241102.1 occurred 66 km west-northwest of Beluga, Alaska, from 04:04 on 1 November 2024 to 02:16 on 5 November 2024. Over 94 hours and 12 minutes, the event sequence registered 85 earthquakes. Magnitudes ranged from -0.8 to 2.9, with the majority of events below magnitude 1.0. Depths were predominantly shallow, clustered between -3 km and 6 km, though isolated events reached 22 km.

The sequence began with low-magnitude events on 1 November, including several at or below magnitude 0.0. Activity intensified on 2 November, featuring the swarm’s largest event of magnitude 2.9 at 03:44:32, followed by additional events up to magnitude 1.9. Subsequent days showed declining frequency and amplitude, with the final recorded event at magnitude -0.6 on 5 November. Depths remained mostly near-surface, consistent with shallow crustal processes.

This swarm represents the eighth recorded sequence in the region during 2024. Historical records since 2000 indicate nine prior swarms, occurring in 2021 (one swarm), 2022 (one swarm), and seven in 2024. Such clustering suggests episodic release of accumulated strain within a tectonically active corridor.

The Beluga area lies in the Cook Inlet basin of south-central Alaska, part of the Alaska-Aleutian subduction zone. Here the Pacific Plate converges with and descends beneath the North American Plate at rates of approximately 6 cm per year. This setting produces both megathrust earthquakes and distributed shallow seismicity. The basin is underlain by Mesozoic accreted terranes and Cenozoic sedimentary fill, with active faults and volcanic centers nearby. The 1964 magnitude 9.2 Great Alaska Earthquake remains the largest recorded event in the broader region, producing extensive surface deformation and aftershock sequences that lasted years.

Earthquake swarms in subduction margins often reflect fluid migration along faults or minor stress perturbations rather than a single mainshock-aftershock cascade. The shallow depths and low magnitudes observed in VS20241102.1 align with this pattern, indicating limited rupture dimensions and rapid energy dissipation.

References

USGS Earthquake Catalog (accessed November 2024)
Alaska Earthquake Center, University of Alaska Fairbanks
Alaska Division of Geological & Geophysical Surveys, Cook Inlet seismic reports