Seismic Swarm S20160821.1 Near Little Lake, California

Seismic swarm S20160821.1 was recorded 5 km NNW of Little Lake, California. The sequence began at 18:17 on 20 August 2016 and concluded at 18:21 on 22 August 2016. Within this 48-hour, 3-minute window, 37 earthquakes were detected.

The events clustered at shallow depths between 0 and 5 km. Magnitudes ranged from -0.1 to 3.0, with the largest shock occurring at 23:44 on 20 August. Most activity consisted of micro-earthquakes below magnitude 1.0, typical of swarm behavior where numerous events occur without a dominant mainshock-aftershock pattern.

The Little Lake area lies within the Eastern California Shear Zone, a region of distributed right-lateral shear between the Pacific and North American plates. This tectonic setting produces frequent small-magnitude seismicity along northwest-trending strike-slip faults. Nearby, the Coso Volcanic Field adds geothermal and magmatic influences that can trigger earthquake swarms through fluid migration and crustal stress changes. The combination of tectonic and volcanic factors explains the recurrent swarm activity observed in the region.

Historical records since 2000 document 52 swarms in the immediate vicinity. Annual counts include four in 2000, five in 2001, two in 2002, seven in 2004, two in 2005, six in 2006, one in 2009, seven in 2010, one in 2011, four in 2012, six in 2013, two in 2014, three in 2015, and two in 2016. These episodes demonstrate persistent seismic restlessness driven by the same geological framework.

Such swarms rarely produce damaging ground motion yet provide valuable data on fault behavior and fluid dynamics. Continued monitoring supports improved understanding of seismic hazards in this tectonically active corridor of eastern California.

References

USGS Earthquake Catalog
California Geological Survey, Regional Fault Maps
SCEC Community Fault Model