Seismic Swarm S20060411.2: Analysis of Activity Near Hawthorne, Nevada

Seismic swarm S20060411.2 was recorded 19 km SSW of Hawthorne, Nevada, beginning at 15:45 on 10 April 2006 and concluding at 23:48 on 11 April 2006. Over 32 hours and 2 minutes, the sequence included 29 earthquakes with magnitudes ranging from 1.2 to 3.2 and focal depths between 0 and 15 km. Most events clustered at depths of 10–13 km, indicating activity along mid-crustal structures typical of the region.

The sequence initiated with modest events on 10 April, including magnitudes of 2.2, 2.3, and 2.5. Activity intensified overnight into 11 April, culminating in the largest shock of magnitude 3.2 at 00:35, followed by a magnitude 2.8 event minutes later. Subsequent events remained below magnitude 2.5, with the final recorded tremor at magnitude 2.6. Depths showed limited variation, though several shallow events at 0–7 km occurred during the later stages.

This swarm reflects episodic strain release common in the western Great Basin. The Hawthorne area lies within the Walker Lane belt, a zone of distributed dextral shear accommodating part of the Pacific–North American plate motion. Extensional faulting along north- to northwest-striking normal faults dominates the local geology, with Quaternary scarps indicating recurrent movement. Historical records document similar swarm-like sequences in the Mina deflection area, where crustal fluids and fault interactions promote clustered seismicity rather than isolated mainshock-aftershock patterns.

Since 2000, only one prior swarm has been identified in the immediate vicinity, occurring in 2001. This low recurrence highlights the episodic nature of swarm activity in the district compared with more persistent background seismicity along the central Nevada seismic belt.

The 2006 swarm produced no reported damage or felt reports beyond the immediate epicentral zone, consistent with its moderate magnitudes and rural setting. Depths predominantly near 11 km align with the brittle-ductile transition in this portion of the Basin and Range, where hydrothermal circulation may facilitate swarm triggering through pore-pressure changes.

Regional tectonics continue to evolve under ongoing extension rates of approximately 1 cm per year. Monitoring by regional networks remains essential for distinguishing swarm behavior from potential foreshock sequences preceding larger events.

References

SeismoSight internal classification records for swarm S20060411.2 parameters and timeline.
USGS Earthquake Hazards Program regional tectonic summaries for western Nevada.
Nevada Bureau of Mines and Geology publications on Quaternary faulting in Mineral County.