Seismic Swarm S20060626.1: Analysis of Activity Near Indian Springs, Nevada

A seismic swarm designated S20060626.1 occurred 52 km west of Indian Springs, Nevada, from 04:06 on 25 June 2006 to 16:23 on 3 July 2006. Over 204 hours and 16 minutes, the event sequence included 129 earthquakes. The first 100 events exhibited magnitudes predominantly between -0.6 and 1.6, with the majority clustering near 0.0 to 0.5. Depths ranged from 2 km to 9 km, averaging approximately 6–7 km, consistent with shallow crustal seismicity in the region.

The sequence began with low-magnitude events on 25 June, including an initial reading of magnitude 0.1 at 8 km depth. Activity intensified later that day with a magnitude 1.6 event at 7 km depth. Subsequent days showed intermittent peaks, such as magnitude 1.3 events on 26 June and 28 June, alongside numerous microearthquakes below magnitude 0.0. Depths remained stable within the upper crust, with occasional shallower occurrences at 2–3 km and deeper ones reaching 9 km. This pattern reflects typical swarm behavior, where numerous small events occur without a dominant mainshock.

The Indian Springs area lies within the Basin and Range Province of southern Nevada, a region defined by extensional tectonics driven by normal faulting. The local geology features Quaternary alluvial deposits overlying Paleozoic carbonate and clastic rocks, with active fault systems accommodating regional extension at rates of 1–2 mm per year. Historical seismic data indicate recurrent swarm activity in this setting, influenced by fluid migration along faults and regional stress fields.

Since 2000, 16 swarms have been recorded in the vicinity. Earlier episodes occurred in 2000 (5 events), 2002 (7 events), 2003 (2 events), and 2005 (2 events). These sequences demonstrate episodic clustering rather than isolated mainshock-aftershock patterns, aligning with the tectonic framework of the central Nevada seismic belt and adjacent Walker Lane.

The 2006 swarm fits established patterns of low-magnitude, shallow-depth activity in this part of Nevada. No events exceeded magnitude 2.0 in the initial 100 readings, underscoring the swarm’s microseismic character. Depths concentrated around 6–7 km suggest nucleation within the seismogenic zone above the brittle-ductile transition.

References

United States Geological Survey Earthquake Catalog
Nevada Seismological Laboratory Regional Reports
Basin and Range Province Tectonic Summaries, Geological Society of America