Seismic Swarm VS20240224.1 Near Pedro Bay, Alaska

A minor seismic swarm designated VS20240224.1 occurred approximately 63 km east-northeast of Pedro Bay, Alaska. The sequence began at 17:45 UTC on 23 February 2024 and concluded at 17:01 UTC on 24 February 2024, spanning 23 hours and 15 minutes. During this period, 30 earthquakes were recorded, all classified as microearthquakes with magnitudes ranging from -0.9 to -0.2. Depths remained consistently shallow, between 0 and 3 km.

The events exhibited a relatively steady rate of occurrence without a dominant mainshock. Initial activity on 23 February included multiple events at magnitude -0.9, clustered in the first few hours. Later phases on 24 February showed slightly varied magnitudes, with the final recorded event at magnitude -0.5. This pattern aligns with typical swarm behavior, where energy release occurs through numerous small events rather than a single larger rupture.

The Pedro Bay region lies within the Cook Inlet basin of south-central Alaska, part of the active Aleutian subduction zone. Here, the Pacific Plate converges with and subducts beneath the North American Plate at rates of approximately 6–7 cm per year. This tectonic setting produces frequent seismicity, including both tectonic and volcanically influenced events. Nearby Iliamna Volcano, an active stratovolcano, contributes to local stress fields that can trigger swarm activity through fluid migration or magmatic processes.

Historical records since 2000 indicate four prior swarms in the immediate area: one each in 2012 and 2016, and two in 2023. These episodes demonstrate recurrent, low-magnitude seismic clustering consistent with the broader regional stress regime. No significant damage or felt reports were associated with the February 2024 swarm, reflecting the limited energy of the recorded events.

Ongoing monitoring by regional seismic networks continues to track activity in this tectonically dynamic zone. Such swarms provide valuable data for understanding subtle strain accumulation and potential precursors to larger events or volcanic unrest.

References

USGS Earthquake Hazards Program – Alaska Seismicity
Alaska Volcano Observatory – Iliamna Region Reports
SeismoSight Internal Swarm Classification Database