Seismic Swarm VS20241130.1: Analysis of Activity Near Tyonek, Alaska

A significant seismic swarm, designated VS20241130.1, occurred 60 km west-northwest of Tyonek, Alaska. The sequence began at 00:47 on 30 November 2024 and concluded at 05:06 on 22 January 2025, spanning 1276 hours and 19 minutes. During this period, 1155 earthquakes were recorded, highlighting elevated seismicity in the Cook Inlet region. The first 100 events reveal predominantly low-magnitude activity, with values ranging from -1.1 to 2.1. Depths were mostly shallow, clustered between 0 and 10 km, though several events reached greater depths, including one at 133 km. Early activity on 30 November featured events such as a magnitude 1.2 quake at 97 km depth and a magnitude 1.4 event at 133 km. Subsequent days showed continued microseismicity, with notable events including a magnitude 2.1 earthquake on 3 December at 4 km depth and multiple magnitude 1.4–1.6 events through early December. This pattern indicates a mix of shallow crustal adjustments and deeper tectonic influences. The Cook Inlet basin lies within a tectonically active zone driven by the subduction of the Pacific Plate beneath the North American Plate along the Aleutian megathrust. This setting produces frequent earthquakes, both shallow and intermediate-depth, as well as associated volcanic activity from the nearby Aleutian arc. Historical records show the region experiences episodic swarms linked to fluid migration or stress transfer along faults. Since 2000, 11 such swarms have been documented in the area, with one in 2021, one in 2022, and nine in 2024 alone. These swarms contribute to ongoing monitoring of seismic hazards in south-central Alaska, where population centers and infrastructure face risks from both local events and potential larger megathrust ruptures. The VS20241130.1 sequence aligns with this established tectonic framework, underscoring the value of continuous seismic surveillance for understanding stress accumulation and release.

References

SeismoSight internal classification data for swarm VS20241130.1.
USGS Earthquake Hazards Program regional tectonic summaries for Cook Inlet, Alaska.