Seismic Swarm S20150908.1: Analysis of Activity Near Walker Lake, Nevada

A notable earthquake swarm, designated S20150908.1, occurred 4 km west of Walker Lake in western Nevada. The sequence began at 22:58 UTC on 7 September 2015 and concluded at 23:52 UTC on 13 September 2015, spanning 144 hours and 53 minutes. During this period, 146 earthquakes were recorded, with detailed parameters available for the first 100 events.

The swarm initiated with a magnitude 0.3 event at 11 km depth. Activity intensified rapidly, culminating in the largest event—a magnitude 4.4 earthquake at 6 km depth on 8 September at 02:15 UTC. Subsequent significant shocks included magnitudes 3.5 and 3.4 within minutes, all at shallow depths around 6–7 km. Magnitudes across the sequence predominantly ranged from 0.0 to 2.0, with depths consistently between 5 and 14 km. A few events registered negative magnitudes or occurred at depths near 0 km, reflecting the sensitivity of local monitoring. The temporal distribution showed peak activity in the initial 24 hours, followed by a gradual decline, characteristic of swarm behavior rather than a classic mainshock-aftershock pattern.

Geologically, the Walker Lake region lies within the Walker Lane belt of western Nevada, a zone of distributed dextral shear that accommodates approximately 20% of the relative motion between the Pacific and North American plates. This belt forms part of the broader Basin and Range Province, where east-west extension drives normal faulting along range-front structures such as those bounding the Wassuk Range. The crust here is relatively thin and warm, facilitating fluid migration that can trigger swarm sequences through pore-pressure changes along favorably oriented faults.

Historical records indicate recurrent swarm activity in the area since 2000, with seven documented episodes prior to 2015. Earlier swarms occurred in 2011 (five events), 2013 (one event), and 2014 (one event). These episodes underscore the region's propensity for clustered seismicity driven by tectonic extension and hydrothermal processes rather than large-magnitude mainshocks.

The 2015 swarm's shallow focal depths and rapid onset align with patterns observed in other Walker Lane sequences, where small-magnitude events often cluster without producing surface rupture. No damage or felt reports beyond minor shaking were associated with the magnitude 4.4 event, consistent with its modest size and rural setting.

This sequence provides insight into ongoing strain accumulation along the western margin of the Great Basin. Continued monitoring remains essential given the proximity to regional infrastructure and the potential for future activity in this tectonically active corridor.

References

Nevada Seismological Laboratory earthquake catalog.
United States Geological Survey Earthquake Hazards Program.
United States Geological Survey Professional Paper on Walker Lane tectonics.