Seismic Swarm S20121218.1: Analysis of Activity Near Goldfield, Nevada

Seismic swarm S20121218.1 occurred 37 km south-southeast of Goldfield in Esmeralda County, Nevada. The sequence began at 04:00 on 17 December 2012 and concluded at 16:18 on 24 December 2012. Over approximately 180 hours, 440 earthquakes were recorded.

Analysis of the first 100 events reveals predominantly low-magnitude activity. Magnitudes ranged from -0.2 to 1.8, with the majority below 1.0. Depths clustered between 4 km and 9 km, although a few events occurred at shallower levels near 0–2 km or deeper intervals up to 14 km. Early activity on 17 December included events at 04:00:58 (M -0.1, 14 km) and 05:45:16 (M 1.8, 8 km). Subsequent days showed continued low-level seismicity, with notable events on 19 December reaching M 1.7 at depths of 7–8 km. The pattern indicates a typical swarm progression of numerous small events without a single dominant mainshock.

This swarm fits into a broader pattern of episodic seismic activity in the region. Since 1 January 2000, nine swarms have been documented in the same area, occurring in 2000, 2001, 2002, 2006, 2007 (two swarms), 2010, and 2011 (two swarms).

The Goldfield area lies within the western Basin and Range Province, characterized by active crustal extension along normal faults. This tectonic setting produces frequent small-magnitude earthquakes and occasional swarms. The locale also forms part of the Walker Lane shear zone, a northwest-trending belt of right-lateral deformation that accommodates a portion of Pacific–North American plate motion. Historical mining districts in the Goldfield region exploited epithermal gold deposits associated with Miocene volcanic activity, but no direct link exists between past mining and current seismicity.

Seismic monitoring in Nevada relies on regional networks operated by the Nevada Seismological Laboratory and the U.S. Geological Survey. These networks provide precise locations and magnitudes for events as small as M 0.0 in well-instrumented areas. Updated catalogs confirm ongoing low-level background seismicity throughout southern Nevada, consistent with the extensional regime.

In summary, swarm S20121218.1 represents a short-lived cluster of microearthquakes typical of the Basin and Range. Continued monitoring supports improved understanding of strain accumulation along regional faults.

References

U.S. Geological Survey Earthquake Hazards Program catalog (usgs.gov/earthquakes)
Nevada Seismological Laboratory regional seismicity reports (seismo.unr.edu)
Basin and Range Province tectonic summaries, USGS Professional Papers