Seismic Swarm S20021126.1 Southwest of Fort Greely, Alaska

The seismic swarm designated S20021126.1 was recorded approximately 81 km southwest of Fort Greely, Alaska. Activity commenced at 21:54 on 25 November 2002 and concluded at 23:57 on 26 November 2002, spanning 26 hours and 3 minutes. During this interval, a total of 30 earthquakes were registered. This swarm represents the earliest event in a sequence of seven swarms documented in the region since 1 January 2000. Earthquake magnitudes within the swarm ranged from 1.0 to 2.9, with focal depths varying between 0 and 14 km. Notable events included a magnitude 2.9 earthquake at a depth of 0 km occurring at 08:07 on 26 November, alongside several magnitude 2.4 events at shallow depths. The majority of activity clustered at depths under 10 km, indicating shallow crustal processes. Geologically, the swarm occurred in proximity to the Denali Fault system, a major right-lateral strike-slip fault that accommodates significant tectonic strain between the Pacific and North American plates. The region lies within the broader tectonically active zone of interior Alaska, characterized by frequent seismic events driven by ongoing plate boundary interactions. On 3 November 2002, a magnitude 7.9 earthquake struck along the Denali Fault just 14 km from the swarm epicentral area, releasing substantial energy and likely influencing subsequent seismic patterns through stress redistribution. Following this major event, the November swarm may reflect aftershock sequences or triggered activity along subsidiary faults. Depths predominantly in the upper crust align with the known seismogenic zone of the Denali Fault, where brittle failure occurs at shallow levels before transitioning to ductile behavior at greater depths. Historical records confirm this swarm as the first of its kind in the post-2000 monitoring period, underscoring episodic clustering in an otherwise diffuse seismic background. Ongoing monitoring by regional networks continues to track such activity, contributing to refined models of fault mechanics in south-central Alaska. The swarm data provide valuable insight into short-term seismic rate changes near major strike-slip structures. References
SeismoSight internal swarm classification records
USGS Earthquake Catalog for Denali Fault events