Seismic Swarm S20080730.1: Analysis of Activity Near Mogul, Nevada

Seismic swarm S20080730.1 occurred approximately 4 km NNW of Mogul, Nevada, a location within the tectonically active Basin and Range province. The sequence began at 10:34 on 29 July 2008 and concluded at 11:40 on 2 August 2008, spanning 97 hours and 6 minutes. During this interval, 76 earthquakes were recorded, with magnitudes ranging from negative values to a peak of 3.2. Depths predominantly clustered between 0 and 8 km, reflecting shallow crustal processes typical of the region.

The swarm initiated with a magnitude 3.2 event at 4 km depth, followed by a rapid succession of smaller shocks. Early activity included events of 0.7, 1.3, and 1.7 magnitude, mostly at 5 km depth. Subsequent tremors showed variable magnitudes, such as 2.4 at 6 km on 29 July and multiple events near 1.0–1.6 on 30 July. Later phases featured a magnitude 2.6 shock at 2 km depth on 1 August, alongside several 1.7–1.9 events. The final recorded event reached magnitude 1.1 at 4 km depth on 2 August. This pattern of clustered, low-to-moderate magnitude quakes without a dominant mainshock exemplifies swarm behavior driven by fluid migration or stress redistribution along local faults.

Mogul lies in western Nevada, where extensional tectonics associated with the Walker Lane belt produce frequent seismic activity. The area features normal faults that accommodate regional extension between the Sierra Nevada and the Great Basin. Historical records indicate that swarm sequences are recurrent here, with ten documented events since 2000. Prior swarms occurred in 2003 (one swarm), 2004 (two), 2005 (two), and 2008 (five), underscoring a pattern of episodic unrest rather than isolated large earthquakes.

Such swarms contribute to ongoing strain release in a zone characterized by Quaternary faulting and moderate seismicity. Depths consistently under 10 km align with brittle failure in the upper crust, influenced by the region's high heat flow and fractured rock. No surface rupture was associated with this sequence, consistent with the modest energy release observed.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Nevada Seismological Laboratory historical data
Basin and Range Province tectonic summaries from USGS Professional Papers