Seismic Swarm S20260101.1: Analysis of Activity Near Yakutat, Alaska

A seismic swarm designated S20260101.1 was recorded 116 km north of Yakutat, Alaska, beginning at 06:46 on 1 January 2026 and concluding at 23:52 on 6 January 2026. Over 137 hours and 5 minutes, the sequence produced 167 earthquakes. The swarm occurred within a tectonically complex zone where the Yakutat terrane collides with the North American plate, generating frequent crustal deformation and seismicity.

Analysis of the first 100 events reveals a rapid onset with the largest shock reaching magnitude 5.7 at a depth of 5 km. Subsequent events included multiple shocks above magnitude 4.0 in the initial hours, followed by a decay into smaller events predominantly between magnitudes 1.5 and 3.5. Depths clustered tightly around 5 km, with occasional shallower or deeper occurrences up to 10 km. The temporal distribution showed highest rates on 1–2 January, tapering thereafter, consistent with swarm behavior driven by fluid migration or stress triggering rather than a single mainshock-aftershock sequence.

Yakutat lies along the southeastern Alaska margin, where oblique convergence between the Pacific and North American plates accommodates slip through a combination of thrust faulting and strike-slip motion. The region forms part of the St. Elias orogen, characterized by rapid uplift and a network of active faults. Historical records indicate elevated background seismicity, with the area capable of producing both moderate swarms and larger events.

Since 2000, four prior swarms have been documented in the vicinity, occurring in 2014 (one swarm) and 2025 (three swarms). These episodes underscore recurrent episodic release of strain within the upper crust.

The January 2026 swarm fits this pattern of clustered activity without evidence of escalation to a major rupture. Depths and magnitudes align with typical shallow crustal events in the terrane, posing low tsunami risk but warranting continued monitoring for aftershock potential.

References

USGS Earthquake Catalog
Alaska Earthquake Center, University of Alaska Fairbanks
Geological Survey of Canada tectonic summaries
SeismoSight internal swarm classification records