Seismic Swarm S20151017.1: Analysis of Activity Near Beatty, Nevada

Seismic swarm S20151017.1 occurred 46 km east-southeast of Beatty, Nevada, in the Basin and Range Province. The sequence began at 17:44 UTC on 16 October 2015 and concluded at 20:48 UTC on 18 October 2015, lasting 51 hours and 4 minutes. During this period, 47 earthquakes were recorded, with magnitudes ranging from -0.5 to 2.4 and focal depths primarily between 6 and 11 km.

The largest event reached magnitude 2.4 at a depth of 10 km on 17 October at 04:08:58 UTC. Most events clustered tightly in both time and space, with 36 occurring within the first 24 hours after initiation. Negative-magnitude events dominated the catalog, reflecting the sensitivity of local seismic networks in this monitored region. Depths remained consistent around 9–10 km for the majority of shocks, consistent with activity along shallow crustal faults.

This swarm fits within a documented pattern of recurrent seismic swarms in the area. Since 1 January 2000, 36 swarms have been identified near Beatty. Annual counts include four in 2000, seven in 2002, two in 2003, two in 2005, one in 2006, two in 2007, seven in 2008, four in 2009, three in 2010, one in 2012, one in 2014, and two in 2015. These episodes typically feature low-magnitude events without a clear mainshock-aftershock sequence, pointing to fluid migration or aseismic slip as possible drivers within the extensional tectonic regime.

The Beatty region lies within the Walker Lane belt, a zone of distributed shear and extension east of the Sierra Nevada. Active normal and strike-slip faults accommodate Basin and Range extension at rates of several millimeters per year. Proximity to the Nevada National Security Site and historical underground nuclear testing has resulted in dense seismic instrumentation, enabling detection of microearthquakes that would otherwise go unnoticed. The Amargosa Desert and surrounding ranges host numerous Quaternary faults capable of producing small swarms through episodic slip on favorably oriented structures.

Regional geology features Paleozoic carbonate and clastic rocks overlain by Tertiary volcanic units and Quaternary alluvium. Groundwater movement along fault zones may contribute to swarm triggering by elevating pore pressures. No surface rupture or damage was associated with S20151017.1, consistent with the low energy release of the sequence.

Seismic monitoring continues to track activity in this portion of southern Nevada, where swarms remain a characteristic expression of ongoing tectonic deformation.

References

USGS Earthquake Catalog
Nevada Seismological Laboratory swarm database
Nevada Bureau of Mines and Geology geologic maps