Seismic Swarm S20190210.1 Near Shungnak, Alaska

Seismic swarm S20190210.1 was recorded 68 km south of Shungnak in northwest Alaska. Activity commenced at 02:21 on 10 February 2019 and concluded at 04:04 on 17 February 2019, spanning 169 hours and 42 minutes. A total of 110 earthquakes were registered during this interval.

Analysis of the first 100 events reveals predominantly shallow focal depths between 0 km and 22 km. Magnitudes ranged from 0.7 to 4.8, with the majority below 2.0. The largest event, magnitude 4.8, occurred at 13:35 on 10 February at 7 km depth. Subsequent notable events included magnitudes 3.6, 3.1, 3.0, and additional 2.8–2.6 events clustered on the first two days. Depths remained consistent within the upper crust, consistent with tectonic release along local fault structures rather than deeper subduction processes.

Northwest Alaska lies within the Arctic Alaska tectonic province, influenced by the broader interaction between the Pacific and North American plates. Although distant from the primary Aleutian subduction zone, the region experiences distributed crustal deformation through strike-slip and thrust faults associated with the Kobuk and related fault systems. Historical seismicity includes moderate events linked to these structures, reflecting ongoing accommodation of strain across the Brooks Range foothills and adjacent basins.

The 2019 swarm exhibited classic swarm characteristics: a rapid onset, lack of a single dominant mainshock-aftershock sequence, and migration of small events over several days. Such sequences are documented across interior and western Alaska and often relate to fluid migration or aseismic slip triggering on pre-existing fractures within Paleozoic and Mesozoic sedimentary and metamorphic rocks.

No damage or felt reports of significance were associated with this swarm, typical for events of this size in a remote area. Continued monitoring by regional seismic networks remains essential for understanding long-term strain patterns in this sparsely instrumented portion of the state.

References
USGS Earthquake Catalog
Alaska Earthquake Center annual reports
Geological Survey of Alaska tectonic framework maps