Seismic Swarm S20060909.2: Analysis of Activity Near Hawthorne, Nevada

Seismic swarm S20060909.2 was recorded 32 km south-southeast of Hawthorne, Nevada, from 10:42 on 8 September 2006 to 15:43 on 9 September 2006. In this 29-hour period, 45 earthquakes were detected, with magnitudes ranging from 0.6 to 2.2 and focal depths primarily between 5 km and 13 km. The sequence began with a magnitude 2.2 event at 5 km depth and concluded with a magnitude 0.6 event at 6 km depth, reflecting typical swarm characteristics of clustered, low-to-moderate magnitude activity without a dominant mainshock.

The temporal distribution showed peak activity during the first evening and overnight hours of 8 September, followed by a gradual decline. Most events clustered between 7 km and 9 km depth, consistent with shallow crustal faulting. Magnitudes remained below 2.0 after the initial pair of 2.2 events, indicating a diffuse energy release distributed across multiple small ruptures rather than progressive failure along a single structure.

This swarm fits into the regional pattern of seismic activity in western Nevada. The location lies within the Walker Lane belt, a zone of distributed right-lateral shear and extension that accommodates a portion of the Pacific-North America plate boundary motion. The belt transects the western margin of the Basin and Range province, where normal faulting and crustal thinning have produced a landscape of north-trending mountain ranges and intervening valleys. Hawthorne sits near the intersection of several active fault systems, including segments of the Wassuk Range fault zone and related structures that have generated both historical and instrumental seismicity.

Since 1 January 2000, three swarms have been documented in the immediate area, with one swarm recorded in 2001 and two in 2006. These episodes underscore the episodic nature of strain release in the region, where fluid migration or aseismic slip on nearby faults can trigger transient clusters of small earthquakes. Depths observed in swarm S20060909.2 align with the brittle-ductile transition zone in this part of the Basin and Range, where temperatures and strain rates permit brittle failure at shallow to mid-crustal levels.

No damage or felt reports of significance were associated with the swarm, consistent with its modest magnitudes. Continued monitoring of the Hawthorne area remains important given its position within an active tectonic corridor that has produced larger events elsewhere in the Walker Lane belt over longer timescales.

References

• U.S. Geological Survey Earthquake Catalog
• Nevada Seismological Laboratory historical records
• SeismoSight internal swarm classification database