Seismic Swarm S20200822.1: Analysis of Activity Near Little Lake, California

Seismic swarm S20200822.1 was recorded in the region 20 km east-southeast of Little Lake, California. The sequence began at 15:06 on 21 August 2020 and concluded at 21:13 on 25 August 2020, spanning 102 hours and 6 minutes. During this period, 66 earthquakes were registered.

The events exhibited magnitudes ranging from -0.5 to 2.8, with the largest shock occurring on 22 August 2020 at 14:30:10. Depths varied between 2 km and 10 km, indicating shallow crustal activity typical of the local tectonic environment. Early events on 21 August clustered around magnitudes of 0.0 to 1.0, followed by a notable increase in both frequency and magnitude on 22 August, including multiple events above magnitude 1.0. Activity persisted at lower levels through 23 and 24 August before tapering off on 25 August, with final notable shocks of magnitude 2.1 and 2.3.

This swarm fits within a broader pattern of seismic activity in the area. Since 1 January 2000, 98 swarms have been documented in the region. Annual counts show variability, with peaks in 2019 (29 swarms) and 2020 (18 swarms), alongside earlier episodes such as 7 swarms each in 2004 and 2010.

The Little Lake area lies within the Eastern California Shear Zone, a zone of distributed right-lateral shear that accommodates a portion of the Pacific-North America plate motion. The local geology features Quaternary volcanic rocks of the Coso Volcanic Field to the north and extensive fault networks, including strands of the Little Lake fault system. These structures have produced historical seismicity linked to Basin and Range extension and Walker Lane deformation. Depths recorded in the swarm align with the brittle upper crust in this extensional regime, where fluid migration or aseismic slip often triggers swarm-like sequences rather than mainshock-aftershock patterns.

Such swarms contribute to ongoing strain release without producing significant surface rupture. Monitoring continues to refine understanding of fault interactions in this tectonically active corridor.

References

SeismoSight internal swarm classification database.
USGS Earthquake Catalog (regional tectonic context).
California Geological Survey fault and seismic hazard maps.