Seismic Swarm S20240513.1: Analysis of Activity Near Nikolski, Alaska

A seismic swarm designated S20240513.1 was recorded 73 km west-southwest of Nikolski, Alaska, in the Aleutian Islands. The sequence began at 06:09 on 12 May 2024 and concluded at 11:26 on 15 May 2024, spanning 77 hours and 16 minutes. During this period, 68 earthquakes were registered.

The events displayed magnitudes ranging from 0.9 to 2.8, with the largest reaching 2.8 at 10:31 on 12 May. Depths varied from negative values indicating possible shallow or surface-proximal activity to a maximum of 15 km. Early activity on 12 May included multiple events around magnitude 2.0 at depths of 3–7 km. Subsequent days showed a mix of shallow (0–2 km) and moderately deeper (7–12 km) shocks, with notable clusters on 13 May featuring repeated magnitudes near 1.5–2.2. Activity tapered on 14–15 May, ending with a magnitude 2.2 event at 9 km depth.

This swarm aligns with patterns observed in the region since 2000, where nine prior swarms have occurred. These include one in 2007, three in 2010, three in 2014, one in 2015, and one in 2023. Such episodic clusters reflect the dynamic stress environment of the Aleutian subduction zone.

Nikolski lies within the Aleutian volcanic arc, formed by the subduction of the Pacific Plate beneath the North American Plate at rates of approximately 6–7 cm per year. This tectonic setting produces frequent seismicity, including both volcanic and tectonic earthquakes, as well as associated volcanic activity. The area features active stratovolcanoes and fault systems that accommodate oblique convergence, contributing to swarm-like sequences driven by fluid migration or stress transfer along the plate interface.

The shallow depths and moderate magnitudes recorded in S20240513.1 are consistent with upper-crustal adjustments common in this convergent margin. No significant damage or tsunami risk was associated with these events, typical for swarms below magnitude 3.0.

Ongoing monitoring by regional networks continues to track aftershock potential and any links to nearby volcanic systems. Historical swarm recurrence underscores the importance of sustained observation in this high-seismicity zone.

References
USGS Earthquake Catalog (regional tectonics data)
Alaska Volcano Observatory (Aleutian arc geology)
SeismoSight internal swarm classification S20240513.1