Seismic Swarm S20070705.1 Near Goldfield, Nevada

A seismic swarm designated S20070705.1 was recorded 33 km south-southeast of Goldfield, Nevada, between 23:17 UTC on 4 July 2007 and 19:54 UTC on 7 July 2007. Over 68 hours and 36 minutes, the sequence produced 47 earthquakes. The largest event reached magnitude 2.2 at a depth of 6 km shortly after the swarm began, while subsequent events ranged from magnitude 0.4 to 1.9 and occurred at depths between 0 and 15 km, with the majority clustered between 2 and 9 km.

The swarm exhibited typical characteristics of low-magnitude, closely spaced events distributed across a short time window. Magnitudes remained below 2.0 after the initial shock, and activity tapered gradually, concluding with a magnitude 0.8 event at 15 km depth. Such patterns are consistent with fluid migration or minor strain release along pre-existing faults within the Basin and Range extensional province.

The Goldfield region lies within Esmeralda County in western Nevada, part of the broader Walker Lane tectonic zone. This area experiences ongoing dextral shear and normal faulting driven by Pacific-North American plate interaction. Historical seismicity in the county includes both mainshock-aftershock sequences and swarm-like episodes, often associated with Quaternary faults and volcanic centers. Since 2000, five swarms have been identified in the immediate vicinity, occurring in 2000, 2001, 2002, 2006, and 2007.

Goldfield itself developed as a major gold-mining district in the early twentieth century, hosted in Miocene volcanic rocks. Regional geology features extensive fault networks that accommodate extension, creating conditions favorable for episodic microseismicity. Depths recorded during the 2007 swarm align with the brittle-ductile transition zone typical of the northern Basin and Range, where most earthquakes nucleate above 15 km.

No damage or felt reports were associated with this low-magnitude sequence, underscoring the value of dense seismic networks in documenting background activity that may precede larger events. Continued monitoring of the Walker Lane remains important for understanding long-term seismic hazard in central Nevada.

References

• U.S. Geological Survey Earthquake Catalog (earthquake.usgs.gov)
• Nevada Seismological Laboratory, University of Nevada, Reno
• USGS Quaternary Fault and Fold Database of the United States