Seismic Swarm S20180207.1: Analysis of Activity South of Hawthorne, Nevada

Seismic swarm S20180207.1 occurred 29 km south of Hawthorne, Nevada, in Mineral County. The sequence began at 10:13 on 7 February 2018 and concluded at 01:05 on 10 February 2018, spanning 62 hours and 52 minutes. During this period, 56 earthquakes were recorded, with magnitudes ranging from -0.2 to 2.5 and focal depths primarily between 6 km and 13 km.

The swarm exhibited typical characteristics of clustered microseismicity, featuring an initial moderate event of magnitude 2.5 on 7 February at 13:39, followed by numerous smaller aftershocks. Activity peaked early in the sequence, with events gradually diminishing in frequency and magnitude over the subsequent days. Notable events included magnitude 1.7 shocks at 10:13 on 7 February and 02:25 on 8 February, alongside many events below magnitude 1.0 that contributed to the overall count.

This swarm aligns with the broader pattern of seismic activity documented in the region since 2000. Historical records indicate 33 swarms in the area through the end of 2017, with notable clusters in 2011 (7 swarms), 2017 (8 swarms), and 2015–2016 (3 swarms each). These recurrent episodes underscore persistent low-level tectonic strain release.

The Hawthorne region lies within the Walker Lane belt, a northwest-trending zone of right-lateral shear accommodating approximately 20% of the relative motion between the Pacific and North American plates. This tectonic setting features numerous north- to northwest-striking faults that facilitate distributed deformation across the Basin and Range Province. Earthquake swarms in this environment often arise from fluid migration or aseismic slip along fault networks rather than mainshock-aftershock sequences driven by a single large rupture.

Geological mapping shows the area underlain by Tertiary volcanic rocks and Quaternary alluvial deposits, with active faults such as those associated with the Wassuk Range and Excelsior Mountains contributing to regional seismicity. Depths of 6–13 km for swarm events correspond to the brittle-ductile transition zone typical of the central Great Basin, where temperatures allow for both brittle failure and ductile flow.

No damage or felt reports were associated with this swarm, consistent with its modest magnitudes. Ongoing monitoring by regional networks continues to track similar sequences, providing data on strain accumulation along the Pacific-North American boundary.

References

USGS Earthquake Hazards Program – Nevada Seismicity
Nevada Bureau of Mines and Geology – Walker Lane Tectonic Summary
SeismoSight Internal Swarm Catalog (S20180207.1)