Seismic Swarm S20181205.1 Near Indian Hills, Nevada

Seismic swarm S20181205.1 was recorded 5 km northeast of Indian Hills, Nevada. The sequence began at 08:31 on 4 December 2018 and concluded at 06:08 on 6 December 2018, spanning 45 hours and 37 minutes. During this interval, 39 earthquakes were detected. The events exhibited magnitudes between -0.1 and 3.2, with the largest event occurring on 4 December 2018 at 15:14:25 UTC. Focal depths ranged primarily from 7 km to 12 km, indicating shallow crustal activity typical of the region. Early events on 4 December were predominantly below magnitude 1.2, followed by the peak magnitude 3.2 shock and subsequent smaller aftershocks. Activity tapered through 5 December, with the final events registering negative magnitudes on 6 December. The swarm occurred in western Nevada, part of the Basin and Range Province. This extensional tectonic regime features normal faulting driven by crustal stretching between the Sierra Nevada and the Colorado Plateau. The local setting also intersects the northern Walker Lane, a zone of distributed right-lateral shear that accommodates a portion of Pacific–North American plate boundary motion. These conditions produce frequent small-magnitude earthquakes and episodic swarms rather than large mainshock-aftershock sequences. Since 2000, four prior swarms have been documented in the same area: one in 2005, two in 2013, and one in 2017. The 2018 swarm aligns with this pattern of recurrent, low-magnitude clustering at similar depths. Seismic monitoring in Nevada benefits from dense regional networks that capture both natural and induced events. Continued observation of such swarms contributes to refined hazard assessments for nearby communities including Carson City and Minden.

References

SeismoSight internal swarm classification S20181205.1
USGS Earthquake Hazards Program regional tectonic summaries
Nevada Seismological Laboratory historical swarm catalog