The 2008 Mogul Earthquake Swarm: Seismic Activity in Western Nevada

The Mogul earthquake swarm of March 2008 occurred approximately 1 km west-northwest of Mogul, Nevada, in Washoe County. Registered by the SeismoSight network as swarm S20080308.1, the sequence began at 09:23 on 8 March 2008 and concluded at 18:23 on 10 March 2008, spanning 56 hours and 59 minutes. During this period, 85 earthquakes were recorded, with magnitudes ranging from -0.3 to 3.2 and focal depths primarily between 0 and 7 km.

The sequence initiated with a magnitude 3.2 event at a depth of 1 km shortly after onset. Subsequent activity consisted predominantly of microearthquakes below magnitude 1.0, accompanied by a few events in the 1.0–2.0 range. Notable larger shocks included magnitudes 1.9 and 1.8 on 9 March at shallow depths of 0–1 km. Depths clustered around 4–6 km for most events, consistent with shallow crustal faulting in the region. The temporal distribution showed peak activity within the first 24 hours, followed by a gradual decline, characteristic of swarm behavior rather than a classic mainshock-aftershock sequence.

Mogul lies within the western Basin and Range Province, where crustal extension along north-south trending normal faults drives regional seismicity. The area forms part of the Walker Lane belt, a zone of distributed shear accommodating Pacific-North America plate motion. Proximity to the Sierra Nevada frontal fault system further elevates seismic hazard. Historical records indicate recurrent swarm activity near Mogul since 2000, with six prior swarms documented: one in 2003, two in 2004, and three in 2005. These episodes reflect ongoing tectonic strain release on local fault networks.

The 2008 swarm contributed to understanding episodic seismicity patterns in the Reno-Tahoe corridor. No significant surface rupture or damage was associated with the events, though the magnitude 3.2 shock was felt locally. Continued monitoring by regional networks supports assessment of evolving seismic hazards in this tectonically active setting.

References

USGS Earthquake Hazards Program
Nevada Seismological Laboratory, University of Nevada, Reno
SeismoSight internal swarm classification records