Seismic Swarm S20230116.2 Near Meadow Lakes, Alaska

A seismic swarm designated S20230116.2 was recorded 11 km north of Meadow Lakes, Alaska, beginning at 17:43 on 16 January 2023 and concluding at 04:06 on 17 January 2023. Over this 10-hour, 22-minute period, 33 earthquakes were detected. The sequence featured a leading magnitude 4.5 event at 34 km depth, followed by numerous smaller shocks with magnitudes predominantly between 1.0 and 1.5 and focal depths ranging from 12 km to 40 km.

The initial shock at 17:43:27 UTC was the largest and deepest of the sequence. Subsequent events clustered between 14 km and 35 km depth, with many occurring in the first two hours. Later activity included isolated events at shallower depths around 12–14 km and a final pair near 04:03 on 17 January. The temporal distribution showed rapid onset after the mainshock, a gradual decline in rate, and termination within half a day, consistent with swarm behavior rather than a classic mainshock-aftershock sequence.

Meadow Lakes lies within south-central Alaska’s Cook Inlet region, where the Pacific Plate subducts beneath the North American Plate along the Aleutian megathrust. This convergent margin produces frequent seismicity at crustal and intermediate depths. The area experiences both shallow crustal earthquakes linked to regional faults and deeper events associated with the subducting slab. Meadow Lakes itself sits atop sedimentary basins that amplify ground motion during larger events.

Alaska remains one of the most seismically active regions in the United States. Since 2000, only one prior swarm has been classified in the same internal catalog, occurring in 2020. The present swarm therefore represents the second such episode in more than two decades for this specific monitoring framework. Regional strain accumulation continues to drive both isolated large earthquakes and occasional clustered sequences like S20230116.2.

Analysis of the depth distribution indicates most events nucleated within the overriding plate and upper portions of the subducting slab. The magnitude 4.5 mainshock likely released accumulated stress along a small fault segment, triggering the subsequent smaller events through static and dynamic stress transfer. No events exceeded magnitude 2.6 after the initial shock, underscoring the swarm’s modest energy release.

Continued monitoring of the Cook Inlet area remains essential given its proximity to population centers and infrastructure. Future swarms in this setting may provide additional insight into stress interactions along the subduction interface and overlying crustal faults.

References

• Alaska Earthquake Center, University of Alaska Fairbanks (updated regional seismicity summaries through 2023)
• U.S. Geological Survey Earthquake Hazards Program (tectonic framework of south-central Alaska)
• SeismoSight internal swarm classification records (S20230116.2 parameters)