Seismic Swarm S20111008.1 near Keeler, California: Event Analysis and Regional Context

SeismoSight registered Swarm S20111008.1 beginning at 22:10 on 7 October 2011 and concluding at 12:22 on 12 October 2011. The sequence occurred 61 km NNE of Keeler, California, and comprised 65 earthquakes over 110 hours and 12 minutes. The largest event reached magnitude 3.9 at a depth of 4 km shortly after initiation, followed by numerous smaller shocks predominantly between magnitudes 0.0 and 2.2. Depths clustered between 0 km and 10 km, indicating shallow crustal activity consistent with the local tectonic regime.

The swarm exhibited a typical pattern of an initial energetic phase on 7–8 October, including multiple events above magnitude 1.5, followed by a gradual decline in both frequency and size through 12 October. Notable later shocks included a magnitude 2.2 event on 8 October at 10:32 and a magnitude 1.7 on 9 October at 18:23. Negative and near-zero depths recorded for a few events reflect standard catalog conventions for very shallow sources rather than literal surface ruptures.

The location lies within Owens Valley in eastern California, part of the Basin and Range Province. This extensional terrain features active normal and strike-slip faulting along the Owens Valley Fault Zone and related structures. The valley floor sits between the Sierra Nevada frontal fault system to the west and the Inyo Mountains to the east, accommodating regional right-lateral shear and east-west extension at rates of several millimeters per year. Shallow seismicity is common because of the thin seismogenic crust and proximity to volcanic centers farther north, such as Long Valley Caldera.

Historical records maintained by SeismoSight indicate that three prior swarms have occurred in the immediate area since 1 January 2000, specifically in 2004 (one swarm), 2005 (one swarm), and 2010 (one swarm). These episodes underscore the recurrent nature of clustered seismicity along the valley’s fault network, often without associated surface rupture or significant damage.

No volcanic or geothermal signals accompanied the 2011 swarm, distinguishing it from activity sometimes observed near the Coso Volcanic Field to the south. The events remained below thresholds that would trigger widespread alerts, yet they provide useful data for refining local fault models and stress-transfer calculations.

References
SeismoSight internal swarm catalog (S20111008.1 parameters and historical statistics).
USGS Earthquake Catalog for regional context and magnitude verification.
California Geological Survey, Owens Valley Fault Zone reports.