Seismic Swarm Analysis: Salcha, Alaska – November 2022

A seismic swarm designated S20221118.1 occurred approximately 19 km west-southwest of Salcha, Alaska, from 20:58 UTC on 17 November 2022 until 10:26 UTC on 19 November 2022. Over 37 hours and 28 minutes, the sequence produced 54 earthquakes, with magnitudes ranging from 0.3 to 4.0 and focal depths between 0 and 16 km. The largest event, magnitude 4.0, occurred at 22:34 UTC on 17 November at a depth of 14 km, followed by a magnitude 3.1 event at 22:50 UTC on 18 November at 9 km depth. Activity showed an initial energetic phase with several events above magnitude 2.0 within the first hours, followed by a gradual decline in both frequency and magnitude.

This swarm represents the sixth documented swarm in the region since 2000. Earlier episodes occurred in 2007 (one swarm), 2011 (one swarm), 2020 (one swarm), and 2021 (two swarms). Such sequences are characteristic of the interior Alaska seismic environment, where distributed crustal faulting produces episodic clusters rather than mainshock-aftershock patterns typical of plate-boundary events.

The Salcha area lies within the Yukon-Tanana terrane of east-central Alaska. Regional seismicity arises primarily from right-lateral strike-slip motion along the Denali Fault system and secondary crustal faults. Depths recorded during the swarm (mostly 0–16 km) align with the brittle upper crust in this intraplate setting. Historical records indicate that interior Alaska experiences moderate-magnitude events capable of local ground shaking, though surface rupture is rare outside the major mapped faults.

The November 2022 swarm did not produce any reported damage or felt reports beyond minor shaking in nearby communities. Continued monitoring by regional networks remains essential given the precedent of recurring swarm activity in the same locale.

References

• Alaska Earthquake Center, University of Alaska Fairbanks
• USGS Earthquake Catalog
• Geological Survey of Alaska – Interior Alaska Seismicity Reports