Seismic Swarm S20080712.1: A Detailed Examination Near Mogul, Nevada

On 12 July 2008, a concentrated seismic swarm designated S20080712.1 was recorded 1 km east of Mogul, Nevada. The sequence began at 01:34 and concluded at 22:03, encompassing 33 earthquakes within a span of 20 hours and 28 minutes. All events were shallow, with depths ranging from 0 to 5 km, and magnitudes remained low, spanning -0.6 to a peak of 1.4. The largest event occurred at 19:11:39 with magnitude 1.4 at 1 km depth, while the majority clustered between -0.5 and 0.3.

The temporal distribution showed initial low-magnitude activity in the early morning hours, followed by a steady continuation through midday and an uptick in the evening. Multiple events registered at depths of 2–3 km, with several at surface level (0 km), indicating activity within the uppermost crust. This pattern aligns with typical swarm behavior, where numerous small events occur without a dominant mainshock.

The Mogul area forms part of western Nevada’s Basin and Range Province, an extensional tectonic regime marked by active normal faulting and distributed deformation. The region experiences recurrent seismic swarms driven by crustal stress adjustments along fault networks. Historical records since 1 January 2000 document 11 such swarms in the vicinity, occurring in 2003 (1 swarm), 2004 (2), 2005 (3), 2007 (1), and 2008 (4). These episodes underscore the area’s persistent low-level seismicity.

Swarm S20080712.1 contributes to the 2008 cluster, highlighting episodic energy release in a zone already prone to fluid-influenced or stress-triggered sequences. Depths consistently under 5 km suggest involvement of near-surface structures rather than deeper crustal processes. The absence of larger events during the swarm reflects the characteristic energy distribution of these sequences, where cumulative moment remains modest.

Ongoing monitoring by regional networks continues to track such activity, aiding in the refinement of seismic hazard assessments for the Reno-Mogul corridor. The 2008 swarm exemplifies the value of dense instrumentation in capturing fine-scale patterns that inform broader understanding of extensional tectonics in the western Great Basin.

References

SeismoSight internal swarm classification records.
Nevada Seismological Laboratory regional monitoring data.
USGS Earthquake Hazards Program tectonic summaries for the Basin and Range Province.