Seismic Swarm S20191214.2: Analysis of Activity Near Little Lake, California
Seismic swarm S20191214.2 occurred approximately 20 km east of Little Lake, California, in a tectonically active region of the Mojave Desert. The sequence began at 03:33 on 14 December 2019 and concluded at 20:56 on 15 December 2019, spanning 41 hours and 22 minutes. During this period, 43 earthquakes were recorded, with magnitudes ranging from 0.3 to 2.8 and focal depths primarily between 3 and 11 km.
The Little Lake area lies within the Eastern California Shear Zone, where northwest-trending strike-slip faults accommodate a portion of the Pacific-North American plate motion. This setting produces frequent low-magnitude seismic swarms driven by both tectonic strain and localized volcanic processes associated with the nearby Coso Volcanic Field. Depths observed in the swarm align with typical brittle failure zones in the upper crust of this region.
The largest event reached magnitude 2.8 at a depth of 4 km on 14 December at 19:31. Other notable shocks included several events of magnitude 1.5–1.8 clustered between 14 and 15 December. Event timing showed an initial burst of activity in the morning of 14 December, followed by a gradual decline with intermittent bursts through the following day. Depths remained shallow overall, consistent with swarm behavior in this part of the shear zone.
Historical records indicate elevated swarm frequency in the area since 2000, with 79 documented swarms through 2019. The year 2019 alone accounted for 28 such sequences, underscoring a period of heightened seismic productivity following the July 2019 Ridgecrest mainshocks. Earlier years with notable activity include 2004 (7 swarms), 2006 (6), and 2010 (7). These patterns reflect the persistent interplay between regional faulting and geothermal influences near Coso.
Such swarms generally pose low hazard to infrastructure but provide valuable data for monitoring strain accumulation and potential volcanic unrest. Continued observation helps refine models of fault interaction in the Eastern California Shear Zone.
References
USGS Earthquake Hazards Program
California Geological Survey
Southern California Seismic Network catalogs