Seismic Swarm S20101204.1: Analysis of Activity Near Mogul, Nevada

Seismic swarm S20101204.1 occurred 12 km south-southeast of Mogul, Nevada, between 07:42 on 3 December 2010 and 05:51 on 5 December 2010. Over 46 hours and 9 minutes, the sequence produced 32 earthquakes. Magnitudes ranged from 0.2 to 2.3, with the largest event recorded at 08:35 on 3 December. Focal depths remained shallow, concentrated between 9 km and 11 km.

The temporal distribution showed initial clustering on 3 December, with 18 events in the first 24 hours, followed by a decline. Events on 4 December totaled 12, and the final two occurred early on 5 December. Depths stayed consistent throughout, indicating a stable source volume without significant migration.

This swarm fits within the established pattern of seismic activity in the Mogul area. Since 1 January 2000, 17 swarms have been documented in the region. Earlier episodes occurred in 2003 (3 swarms), 2004 (2), 2005 (4), 2007 (1), and 2008 (7). These recurrent swarms reflect ongoing tectonic strain release along local fault structures.

Mogul lies in western Nevada within the Walker Lane belt, a zone of distributed right-lateral shear that accommodates part of the Pacific–North American plate boundary motion. The belt forms the western margin of the Basin and Range Province, where crustal extension produces north–south trending normal faults. Seismicity in this setting typically occurs at depths of 5–15 km, consistent with the observed 9–11 km range. Regional geology features Quaternary alluvial deposits overlying Mesozoic basement rocks, with active faults capable of both swarm-type sequences and larger mainshock–aftershock events.

Historical records indicate that the Mogul area has experienced multiple swarms over recent decades, underscoring its elevated background seismicity relative to stable continental interiors. Such activity arises from the interplay of extensional faulting and minor strike-slip components, allowing fluid migration or aseismic slip to trigger successive small events without a dominant mainshock.

Continued monitoring of similar sequences provides valuable data on strain accumulation and release in the Walker Lane. The 2010 swarm, though modest in magnitude, contributes to the long-term characterization of seismic hazards in this tectonically active corridor.

References

USGS Earthquake Hazards Program – Walker Lane tectonics overview
Nevada Seismological Laboratory – Regional fault maps and historical seismicity
Nevada Bureau of Mines and Geology – Geological framework of western Nevada