Seismic Swarm S20121012.1: Analysis of Activity Near Spanish Springs, Nevada
Seismic swarm S20121012.1 occurred 2 km northeast of Spanish Springs, Nevada, from 08:05 on 11 October 2012 to 13:58 on 15 October 2012. Over 101 hours and 52 minutes, the sequence produced 108 earthquakes. The first 100 events exhibited magnitudes ranging from -0.7 to 1.1, with the majority falling between -0.3 and 0.6. Depths clustered tightly around 9–13 km, though isolated events reached as shallow as 3 km and as deep as 14 km.
Temporal distribution showed initial sparse activity on 11 October, followed by sustained elevated rates through 12–14 October. No single dominant mainshock emerged; instead, the sequence displayed typical swarm characteristics with numerous events of similar size occurring in rapid succession. The largest recorded magnitude of 1.1 occurred on 12 October at 03:59, accompanied by several events of magnitude 0.8 and 1.0 on subsequent days.
Spanish Springs lies within the northern Walker Lane belt, a zone of distributed dextral shear and extension east of the Sierra Nevada. This tectonic setting forms part of the broader Basin and Range Province, where ongoing crustal extension occurs along north- to northwest-striking normal faults. Regional strain rates remain moderate to high, driven by Pacific–North American plate interaction. Earthquake depths near 10 km align with the brittle–ductile transition typical of the area’s seismogenic crust.
Historical records indicate that swarm activity has been recurrent in this portion of western Nevada. Since 1 January 2000, six distinct swarms have been documented, with the earliest occurring in 2008. These episodes underscore the region’s propensity for clustered seismicity rather than isolated large-magnitude events.
The 2012 swarm’s shallow to mid-crustal depths and low magnitudes are consistent with fluid-driven or aseismic-slip-triggered mechanisms commonly observed in the Walker Lane. Such swarms contribute to long-term strain release without producing significant surface rupture.
References
- USGS Earthquake Catalog (ComCat)
- Nevada Seismological Laboratory regional reports
- SeismoSight internal swarm classification database