Seismic Swarm Analysis: April 2017 Event Near Hawthorne, Nevada

An earthquake swarm designated S20170413.1 occurred 29 km south-southwest of Hawthorne, Nevada, from 11:58 on 13 April 2017 until 11:11 on 29 April 2017. During this 383-hour period, 587 events were recorded. The sequence exemplifies typical swarm behavior in the western Great Basin, where clusters of small-magnitude earthquakes occur without a single dominant mainshock.

Analysis of the first 100 events reveals magnitudes ranging from 0.1 to 3.1, with the largest event reaching magnitude 3.1 at a depth of 3 km. Depths predominantly fell between 1 km and 15 km, centering around 5–8 km. Early activity showed rapid onset, with multiple events exceeding magnitude 2.0 within the first several hours, followed by a gradual decline in both rate and peak magnitude. Depths remained shallow throughout, consistent with brittle failure in the upper crust.

The Hawthorne area lies within the Walker Lane belt, a zone of distributed right-lateral shear accommodating approximately 20 % of Pacific–North America plate motion. This tectonic setting produces abundant normal and strike-slip faulting across the Basin and Range Province. Regional seismicity is driven by northwest-directed extension superimposed on the broader transform boundary, resulting in frequent earthquake swarms rather than isolated large events.

Historical records indicate 15 swarms have occurred in the region since 1 January 2000. These include one swarm in 2001, two in 2006, seven in 2011, one in 2013, three in 2016, and the 2017 sequence itself. Such recurrence underscores persistent strain accumulation along local fault networks.

Swarm activity in this portion of Nevada is commonly linked to fluid migration or aseismic slip on favorably oriented faults. Depths observed in the 2017 sequence align with the seismogenic zone documented across the central Walker Lane. No surface rupture or damage was associated with the events, typical for swarms composed of events below magnitude 4.

Continued monitoring by regional seismic networks remains essential for distinguishing swarm sequences from foreshock activity preceding larger earthquakes. The 2017 Hawthorne swarm contributes to the growing catalog used to refine probabilistic seismic hazard assessments for Mineral County and surrounding communities.

References

USGS Earthquake Hazards Program – Nevada Seismicity
Nevada Seismological Laboratory – Regional Tectonic Summary
UNR SeismoSight internal swarm classification data