Seismic Swarm Activity Near Goldfield, Nevada: July 2010

An earthquake swarm designated S20100703.1 was recorded 39 km south-southeast of Goldfield, Nevada, beginning at 09:02 on 3 July 2010 and concluding at 12:05 on 4 July 2010. Over this 27-hour period, 38 events were detected, providing a detailed record of localized seismic activity in a tectonically active portion of the Basin and Range Province.

The events displayed a narrow magnitude range, with the largest reaching 2.9 and the smallest registering negative values indicative of microseismicity. Depths clustered predominantly between 5 and 10 km, consistent with shallow crustal faulting typical of the region, although isolated events extended to 18 km and one occurred at the surface. Activity peaked in the first several hours, with multiple events exceeding magnitude 1.0 occurring within minutes of the onset, followed by a gradual decline through the afternoon and evening of 3 July before a final event on 4 July.

This swarm fits within a broader pattern of episodic seismic clusters observed in the area. Since 1 January 2000, six such swarms have occurred near Goldfield, with earlier episodes recorded in 2000, 2001, 2002, 2006, and two in 2007. These recurrent swarms reflect ongoing strain accommodation along normal faults that characterize the extensional regime of western Nevada.

The Goldfield region occupies the western Basin and Range Province, where crustal extension has produced a series of north-trending mountain ranges and intervening valleys since the Miocene. Seismicity arises primarily from movement on high-angle normal faults that accommodate east-west stretching at rates of several millimeters per year. Historical mining activity in the Goldfield district has documented minor ground shaking, yet modern instrumental records show that most events remain below damaging thresholds.

Analysis of the July 2010 sequence reveals a classic swarm signature: rapid onset, absence of a single dominant mainshock, and a high proportion of small-magnitude events distributed over a compact volume. Depths indicate rupture within the seismogenic upper crust, while the temporal decay suggests fluid migration or aseismic slip may have contributed to triggering successive events.

Continued monitoring by regional seismic networks remains essential for distinguishing background tectonic release from potential precursors to larger earthquakes. The documented recurrence of swarms underscores the persistent, low-level seismic hazard in this portion of Nevada.

References

• U.S. Geological Survey Earthquake Hazards Program, Nevada Seismicity
• Nevada Bureau of Mines and Geology, Basin and Range Tectonics
• Western States Seismic Policy Council, Regional Earthquake Data Summaries