Seismic Swarm Activity Near Adak, Alaska: March 2025

A seismic swarm designated PS20250320.1 occurred approximately 93 km south-southeast of Adak, Alaska, within the tectonically active Aleutian Islands region. The sequence began at 08:13 on 19 March 2025 and concluded at 06:25 on 20 March 2025, spanning 22 hours and 12 minutes. During this period, five earthquakes were recorded, with magnitudes ranging from 2.6 to 5.6 and focal depths between 13 km and 35 km.

The events unfolded as follows: a magnitude 5.0 earthquake at 13 km depth on 19 March at 08:13, followed on 20 March by a magnitude 5.6 event at 17 km depth (04:28), a magnitude 5.4 event at 35 km depth (05:13), a magnitude 5.2 event at 20 km depth (06:07), and a magnitude 2.6 event at 35 km depth (06:25). This swarm reflects typical clustered seismicity in subduction zones, where stress release occurs through multiple moderate events rather than a single large rupture.

The location lies along the Aleutian subduction zone, where the Pacific Plate converges with and subducts beneath the North American Plate at rates of approximately 6–7 cm per year. This tectonic setting drives frequent seismic and volcanic activity across the arc. The region features a chain of volcanic islands formed by magma generated from the descending slab, with notable volcanoes such as those near Adak contributing to the area's geological complexity. Historical records indicate persistent seismicity, consistent with the zone's role as one of the most earthquake-prone areas globally.

Since 2000, the vicinity has experienced 61 documented swarms, with notable yearly occurrences including 15 in 2020, 11 in 2018, and 6 each in 2013 and 2021. These swarms often precede or accompany larger tectonic adjustments. A significant event in the broader area was the magnitude 7.0 earthquake on 30 August 2013, located 101 km southwest of Atka and approximately 77 km from the recent swarm center. Such activity underscores the ongoing potential for moderate-to-large earthquakes in the Aleutians.

Monitoring by seismic networks continues to track these patterns, aiding in hazard assessment for nearby communities. The swarm's characteristics align with subduction-related processes involving fluid migration and fault interactions at intermediate depths.

References

• USGS Earthquake Catalog (earthquake.usgs.gov)
• Alaska Earthquake Center (aeic.alaska.edu)
• NOAA National Centers for Environmental Information (ncei.noaa.gov)