Seismic Swarm S20110704.1: Earthquake Activity near Hawthorne, Nevada

Seismic swarm S20110704.1 was recorded 35 km south-southwest of Hawthorne, Nevada. The sequence began at 19:00 on 3 July 2011 and concluded at 15:33 on 7 July 2011, spanning 92 hours and 32 minutes. During this interval, 49 earthquakes were detected, with magnitudes ranging from 0.5 to 1.9 and focal depths between 9 km and 13 km. The majority of events clustered near 10 km depth, consistent with shallow crustal seismicity typical of the area.

Event timing showed an initial peak on 4 July, followed by sustained low-level activity through 6 July and a final event on 7 July. The largest shocks reached magnitude 1.9 on 4 July at 20:58 and again on 6 July at 16:01. No events exceeded magnitude 2.0, indicating a swarm characterized by numerous small-magnitude earthquakes rather than a mainshock-aftershock sequence.

This swarm forms part of a broader pattern observed in the Hawthorne region. Since 1 January 2000, nine swarms have occurred, distributed across 2001 (two events), 2004 (one), 2006 (three), and 2011 (three). The repeated occurrence of swarm-type activity highlights episodic seismic release along local fault structures.

The Hawthorne area lies within the western Basin and Range Province, where crustal extension drives normal and strike-slip faulting. Regional tectonics are influenced by the Walker Lane belt, a zone of distributed shear accommodating part of the Pacific-North America plate motion. Earthquake depths of 9–13 km align with the seismogenic zone in this extensional regime, where brittle failure occurs above the brittle-ductile transition.

SeismoSight internal classification designates swarm S20110704.1 as a distinct cluster based on spatiotemporal criteria. Such sequences are monitored to assess background seismicity levels and potential links to fluid migration or fault interaction within the regional network of Quaternary faults.

References

SeismoSight internal swarm database
USGS Earthquake Catalog (regional context)