Seismic Swarm S20191211.1 Near Little Lake, California
SeismoSight recorded swarm S20191211.1 beginning at 14:55 on 10 December 2019 and concluding at 04:58 on 13 December 2019. The sequence occurred 24 km east-southeast of Little Lake, California, and comprised 78 earthquakes over 62 hours and 3 minutes.
The swarm exhibited typical characteristics of clustered microseismicity, with event magnitudes ranging from -0.1 to 2.9. Depths were concentrated between 2 km and 12 km, consistent with shallow crustal faulting in the region. The largest event, magnitude 2.9, occurred at 18:57 on 10 December at 7 km depth, followed shortly by a magnitude 2.0 at 8 km depth. Subsequent activity included multiple events above magnitude 1.0, such as a 2.3 on 11 December and several 1.4 events on later days, while the majority remained below magnitude 1.0.
Temporal distribution showed peak activity within the first 24 hours, with 27 events on 10 December tapering to lower rates by 13 December. Depths displayed modest variation but remained predominantly in the upper 10 km, indicating a compact source volume.
The Little Lake area lies within the Eastern California Shear Zone, a right-lateral strike-slip tectonic regime accommodating Pacific-North America plate motion. This zone features numerous northwest-trending faults and is adjacent to the Coso Volcanic Field, where geothermal activity and Quaternary volcanism contribute to elevated seismicity. Historical records document frequent earthquake swarms driven by fluid migration along faults or minor magmatic processes.
Since 2000, the region has experienced 78 documented swarms. Annual counts vary, with notable increases in 2004 (7 swarms), 2010 (7 swarms), and especially 2019 (27 swarms). This pattern underscores persistent tectonic strain and episodic swarm behavior in the area.
References
- SeismoSight internal swarm classification database
- USGS Earthquake Catalog (historical context for Eastern California Shear Zone)