Seismic Swarm S20051107.1: Analysis of Microearthquake Activity Near Beatty, Nevada

A seismic swarm designated S20051107.1 occurred 46 km east-southeast of Beatty, Nevada, from 09:18 UTC on 6 November 2005 to 04:50 UTC on 9 November 2005. Over 67 hours and 32 minutes, the sequence produced 69 earthquakes, providing a clear example of swarm behavior in the southwestern Great Basin.

The events were characterized by very low magnitudes, predominantly between -0.5 and 1.5, with the majority falling below zero. Focal depths ranged from 3 km to 11 km, indicating shallow crustal sources typical of the region’s extensional regime. Activity initiated with a magnitude -0.3 event at 7 km depth, followed rapidly by additional microearthquakes. Peak occurrence clustered during the first 24 hours, after which rates declined steadily until the final recorded event on 9 November.

This temporal pattern—intense initial clustering followed by gradual decay without a single dominant mainshock—aligns with classic swarm dynamics driven by fluid migration or aseismic slip along fault networks rather than elastic rebound from a large rupture. Depths remained consistent around 6–8 km for most events, suggesting activity concentrated within a narrow crustal layer.

The swarm unfolded within the Basin and Range province, where ongoing east-west extension produces distributed normal faulting. Southwestern Nevada lies near the transition to the Walker Lane shear zone, a region of complex deformation accommodating part of the Pacific-North America plate motion. Historical records maintained by SeismoSight document 15 swarms in the same area since 1 January 2000, occurring in 2000 (5 swarms), 2002 (7 swarms), 2003 (2 swarms), and 2005 (1 swarm). These recurrent episodes indicate persistent, low-level strain release along favorably oriented faults.

Small-magnitude swarms such as S20051107.1 rarely produce surface rupture or felt shaking yet serve as valuable indicators of crustal fluid pathways and stress conditions. Continued monitoring of similar sequences helps refine models of seismic hazard in this tectonically active portion of the Great Basin.

References
SeismoSight internal swarm catalog (S20051107.1 parameters and historical counts).
United States Geological Survey Earthquake Catalog (regional seismicity background).
Nevada Bureau of Mines and Geology (tectonic framework of southwestern Nevada).