Seismic Swarm S20161218.1: Analysis of Activity Near Pahrump, Nevada

A seismic swarm designated S20161218.1 occurred approximately 49 km north-northwest of Pahrump, Nevada, from 14:25 on 17 December 2016 to 15:29 on 18 December 2016. Over this 25-hour period, 27 earthquakes were recorded. Magnitudes ranged from -0.7 to 1.6, with focal depths between 7 km and 11 km. The sequence began with low-magnitude events clustered around 14:25 and 14:34 on 17 December, followed by additional activity in the evening hours. A notable uptick occurred near 03:01 on 18 December with the largest event of magnitude 1.6 at 11 km depth. Subsequent events remained small and shallow, concluding with a magnitude -0.1 event at 15:29 on 18 December.

This swarm exemplifies typical characteristics of seismic swarms in the region, where numerous events occur without a dominant mainshock. The events clustered tightly in both time and space, with most magnitudes below 0.5 and depths averaging near 10 km. Such patterns often reflect distributed stress release along minor faults rather than a single rupture.

The Pahrump area lies within the Basin and Range Province of southern Nevada, an extensional tectonic regime marked by north-south trending normal faults and active crustal stretching. This geological setting results from the broader interaction between the Pacific and North American plates, with additional influence from the Walker Lane shear zone to the west. Historical seismicity in Nye County includes frequent small-magnitude earthquakes, consistent with ongoing extension and possible contributions from hydrothermal fluid movement at depth.

Since 1 January 2000, the region has experienced 36 documented swarms. Yearly distribution shows variability: four swarms in 2000, five in 2002, two in 2003, two in 2005, one in 2006, two in 2007, five in 2008, four in 2009, three in 2010, one in 2012, one in 2013, one in 2014, three in 2015, and two in 2016. These recurrent swarms indicate persistent low-level seismic productivity tied to the local fault network.

The December 2016 swarm aligns with this established pattern of episodic, low-magnitude activity. Depths in the 7–11 km range suggest involvement of mid-crustal structures typical of Basin and Range normal faulting. No damage or felt reports were associated with the events, reflecting their small sizes.

Continued monitoring of such swarms provides insight into the evolving stress field and potential for larger events in this tectonically active portion of Nevada.