Seismic Swarm S20120623.1: Analysis of Activity Near Incline Village, Nevada

Swarm S20120623.1 was recorded 7 km north of Incline Village, Nevada, beginning at 20:07 on 22 June 2012 and concluding at 10:05 on 24 June 2012. Over 37 hours and 57 minutes, the sequence produced 37 earthquakes. The events clustered tightly in time and space, characteristic of swarm behavior where no single mainshock dominates.

The sequence opened with a magnitude 2.0 event at 7 km depth. Activity intensified early on 23 June with a magnitude 4.2 earthquake at 6 km depth, followed within minutes by several smaller events ranging from magnitude 2.1 to 0.4 at depths of 3–5 km. Subsequent events remained mostly below magnitude 2.0, with occasional larger shocks including a magnitude 2.0 at 6 km and a magnitude 2.5 at 6 km later that morning. Depths throughout the swarm ranged from 0 km to 7 km, indicating shallow crustal sources. The final recorded event was a magnitude 0.1 earthquake at 5 km depth.

This swarm fits a pattern of recurrent seismic activity in the region. Since 1 January 2000, 19 swarms have occurred near Incline Village. Earlier episodes were documented in 2003 (3 swarms), 2004 (2), 2005 (4), 2007 (1), 2008 (7), 2010 (1), and 2012 (1, the present sequence).

The Incline Village area lies within the northern Sierra Nevada, near the transition to the Basin and Range Province. This setting features active normal and strike-slip faulting associated with regional extension and shear. The Lake Tahoe basin is bounded by faults capable of producing moderate earthquakes, and shallow seismicity is common due to the thin seismogenic crust. Historical records show that similar swarms have occurred without producing damaging ground motion, though the magnitude 4.2 event reached levels that could be felt locally.

Ongoing monitoring by regional seismic networks continues to track microseismicity in the Tahoe-Sierra region, providing data on fault behavior and stress accumulation. Such swarms offer insight into the distributed deformation that characterizes this portion of the western United States.

References
SeismoSight internal swarm classification database.
United States Geological Survey Earthquake Hazards Program regional reports on the northern Sierra Nevada.
Nevada Seismological Laboratory summaries of Lake Tahoe basin tectonics.