Seismic Swarm S20001122.1 Near Pahrump, Nevada: Geological Context and Event Analysis

The seismic swarm designated S20001122.1 occurred 39 km northwest of Pahrump in Nye County, Nevada. It began at 20:39 UTC on 21 November 2000 and concluded at 03:02 UTC on 23 November 2000. Over 30 hours and 22 minutes, the swarm produced 42 earthquakes. This event represents the first swarm recorded in the region since 1 January 2000, with only one additional swarm documented in the subsequent period.

Pahrump lies within the southern Basin and Range province, a tectonically active extensional domain characterized by north-south trending mountain ranges separated by sediment-filled valleys. Regional deformation occurs primarily along normal faults associated with crustal stretching, though the broader Walker Lane belt to the west introduces a component of right-lateral shear. The local geology features Quaternary alluvium overlying Paleozoic carbonate and siliciclastic rocks, with several mapped faults capable of producing small to moderate earthquakes. Depths of recorded events in this swarm ranged from 0 to 9 km, consistent with shallow seismicity typical of the upper crust in this area.

The swarm initiated with a magnitude 3.0 earthquake at 5 km depth. Subsequent activity included events of magnitude 2.3 at 21:32 and 2.3 at 02:30 on 22 November, both at 5 km depth. Magnitudes generally remained below 1.0 after the first several hours, with many events registering between 0.0 and 0.9. A notable late event of magnitude 2.0 occurred at 06:43 on 22 November at 3 km depth. The sequence showed no clear migration pattern but maintained a tight spatial clustering around the reported epicentral area.

Shallow focal depths throughout the swarm suggest brittle failure within the uppermost few kilometers of crust, where fluid migration or stress triggering along minor faults may have contributed to the clustered occurrence. No damage or felt reports beyond instrumental detection were associated with the activity.

This swarm provides insight into the low-level, episodic seismicity that characterizes the Pahrump region. Continued monitoring remains essential given the proximity to populated areas and infrastructure along the Nevada-California border.

References

SeismoSight internal swarm classification S20001122.1 USGS Earthquake Catalog (regional tectonic framework)