Seismic Swarm S20220207.1: Activity Near Rachel, Nevada

Seismic swarm S20220207.1 occurred approximately 50 km south-southwest of Rachel, Nevada, within the Basin and Range Province. The sequence began at 02:36 UTC on 7 February 2022 and concluded at 08:05 UTC on 8 February 2022, spanning 29 hours and 28 minutes. During this interval, 38 earthquakes were recorded, with the majority exhibiting magnitudes below 1.0 and focal depths ranging from 6 to 9 km.

The largest event reached magnitude 2.9 at 02:38 UTC on 7 February, followed by a magnitude 2.0 shock at 02:44 UTC and a magnitude 2.2 event at 06:45 UTC the same day. Remaining events displayed low to negative magnitudes, consistent with microseismicity typical of swarm sequences. Depths clustered tightly around 7 km, suggesting a shallow crustal source likely influenced by regional extensional stresses.

This swarm represents the fourth documented episode in the area since 2000, following isolated swarms in 2012, 2015, and 2019. Such recurrent patterns indicate persistent, low-level tectonic strain release along local fault structures without progression to a mainshock-aftershock sequence.

The Rachel region lies in a tectonically active portion of the Great Basin, where northwest-southeast extension along normal faults accommodates crustal thinning at rates of several millimeters per year. Historical seismicity in southern Nevada reflects this framework, with distributed small-magnitude events often linked to fluid migration or stress perturbations on pre-existing fractures. Depths of 6–9 km align with the brittle-ductile transition zone in this province, where most regional earthquakes nucleate.

No damage or felt reports were associated with the 2022 swarm, underscoring its minor energy release relative to larger Basin and Range events. Continued monitoring remains essential given the area's proximity to critical infrastructure and the potential for future swarm reactivation.

References

SeismoSight internal swarm catalog S20220207.1
USGS Earthquake Hazards Program regional tectonic summaries
Nevada Seismological Laboratory historical earthquake database