Seismic Swarm S20240119.1 Near Salcha, Alaska

A notable earthquake swarm designated S20240119.1 occurred 3 km south-southwest of Salcha, Alaska, beginning at 21:34 on 19 January 2024 and concluding at 14:23 on 7 February 2024. Over 448 hours and 49 minutes, the swarm produced 680 earthquakes, highlighting ongoing seismic activity in Interior Alaska.

The sequence initiated with a magnitude 5.3 event at a depth of 10 km. Subsequent events included a magnitude 3.7 shock three minutes later, followed by a rapid succession of smaller tremors. Analysis of the first 100 events reveals a concentration of activity in the initial hours, with magnitudes predominantly between 0.7 and 3.4 and focal depths ranging from 0 to 11 km. The largest events clustered early in the swarm, while later occurrences trended toward lower magnitudes below 2.0. Depths remained consistently shallow, suggesting brittle failure within the upper crust rather than deeper subduction-related processes.

This swarm aligns with the tectonic setting of the region. Salcha lies in a zone of distributed crustal deformation in central Alaska, where the Denali Fault and associated structures accommodate right-lateral strike-slip motion driven by oblique convergence between the Pacific and North American plates. Historical records indicate moderate background seismicity, punctuated by episodic swarms that release accumulated strain without producing a single dominant mainshock-aftershock sequence.

Since 1 January 2000, five prior swarms have been documented in the immediate area. These occurred in 2011 (one swarm), 2020 (one swarm), 2021 (two swarms), and 2022 (one swarm). The 2024 event represents the sixth such episode, underscoring a recurring pattern of clustered seismicity that may reflect fluid migration or stress triggering along local fault networks.

Overall, Swarm S20240119.1 exemplifies the persistent, low-to-moderate seismic hazard in this part of Alaska. Continued monitoring remains essential for refining models of crustal behavior and assessing potential links to larger regional events along the Denali Fault system.

References

Alaska Earthquake Center, University of Alaska Fairbanks.
USGS Earthquake Hazards Program regional reports.