Seismic Swarm S20130726.1: Analysis of Activity Near Hawthorne, Nevada

A seismic swarm designated S20130726.1 occurred 14 km southwest of Hawthorne, Nevada, between 05:13 UTC on 26 July 2013 and 02:51 UTC on 27 July 2013. The sequence lasted 21 hours and 37 minutes and comprised 29 earthquakes. The largest event reached magnitude 3.0 at a depth of 3 km, while the remaining events ranged from magnitude 0.1 to 2.1 and occurred at depths between 0 km and 28 km. Most activity clustered at shallow depths of 0–5 km, with a few deeper events up to 28 km.

The swarm exhibited typical characteristics of clustered microseismicity, beginning with the magnitude-3.0 mainshock followed by numerous smaller aftershocks. Events occurred in rapid succession during the first several hours, then tapered off toward the end of the sequence. Depths remained predominantly crustal, consistent with regional faulting patterns that accommodate extension and shear.

Hawthorne lies in western Nevada within the Walker Lane belt, a northwest-trending zone of distributed right-lateral shear that accommodates approximately 20 percent of Pacific–North America relative plate motion. This tectonic setting produces abundant normal and strike-slip faulting, resulting in frequent small-magnitude earthquakes and occasional swarms. The area forms part of the broader Basin and Range Province, where crustal extension has created a landscape of north-trending mountain ranges separated by sediment-filled valleys. Active faults in the region include segments of the Wassuk Range fault system and related structures capable of producing both isolated events and swarm-like sequences.

Historical records maintained by SeismoSight indicate that 12 swarms have occurred in the same locale since 1 January 2000. These include one swarm in 2001, three in 2006, seven in 2011, and one in 2012. The 2013 swarm fits the established pattern of episodic, low-magnitude clustering that does not appear to culminate in a larger mainshock.

Such swarms are commonly attributed to fluid migration or aseismic slip along favorably oriented faults within the actively deforming Walker Lane. Although individual events rarely cause damage, the cumulative ground motion can be felt locally and provides valuable data for refining seismic hazard models. Continued monitoring by regional networks helps distinguish swarm behavior from foreshock sequences that might precede a larger earthquake.

References

• Nevada Seismological Laboratory, University of Nevada, Reno – Regional seismicity catalog and tectonic framework reports.
• USGS Earthquake Hazards Program – Walker Lane tectonic summaries and Basin and Range Province geological overviews.
• SeismoSight internal swarm classification database (S20130726.1 parameters used as provided).