Seismic Swarm S20110418.1: Analysis of Activity Near Goldfield, Nevada

Seismic swarm S20110418.1 occurred 41 km south-southeast of Goldfield, Nevada, beginning at 19:25 on 17 April 2011 and concluding at 07:44 on 20 April 2011. Over this 60-hour period, 62 earthquakes were recorded. The events clustered in a compact spatiotemporal window, with the majority occurring on 18 April. Magnitudes ranged from -0.2 to 2.6, and focal depths extended from the surface to 19 km, though most clustered between 5 km and 9 km. The largest event, magnitude 2.6, took place at 05:17 on 18 April at 7 km depth. Subsequent notable shocks included a magnitude 2.5 at 14:05 the same day. Activity showed two main pulses on 18 April, separated by several hours of relative quiescence, followed by a rapid decline on 19–20 April. This swarm exemplifies typical characteristics of low-magnitude, shallow seismic sequences in the region. Depths predominantly under 10 km align with brittle failure within the upper crust, while the narrow magnitude distribution indicates a swarm rather than a mainshock-aftershock sequence. No events exceeded magnitude 3, consistent with background strain release rather than significant tectonic loading. The Goldfield area lies in Esmeralda County within the western Basin and Range Province. This tectonic domain experiences active crustal extension accommodated by normal and strike-slip faults. The local geology comprises Tertiary volcanic rocks overlying Paleozoic sedimentary units, with numerous mapped faults that facilitate fluid migration and episodic seismicity. Historical mining in the Goldfield district exploited epithermal gold deposits hosted in these volcanic rocks, but the seismic record reflects ongoing tectonic processes unrelated to anthropogenic activity. Since 2000, eight prior swarms have been documented in the same general vicinity, occurring in 2000, 2001, 2002, 2004, 2006, 2007 (two events), and 2010. This recurrence suggests persistent low-level strain accumulation along local fault networks, modulated by fluid involvement or aseismic slip transients common in the Walker Lane transition zone east of the Sierra Nevada. Overall, swarm S20110418.1 represents routine background seismicity that poses negligible hazard but contributes to understanding the distributed deformation across central Nevada. Continued monitoring remains essential for refining probabilistic hazard assessments in this extensional setting.

References

• Nevada Seismological Laboratory earthquake catalog (internal swarm classification S20110418.1)
• USGS Earthquake Hazards Program regional tectonic summaries for the Basin and Range Province