Earthquake Swarm S20191011.1: Seismic Activity Near Little Lake, California
The region surrounding Little Lake in Inyo County, California, lies within the Eastern California Shear Zone, a tectonically active area characterized by northwest-trending strike-slip faults and distributed deformation between the Pacific and North American plates. This zone experiences frequent seismic events due to its position at the intersection of the Sierra Nevada frontal fault system and the Garlock Fault. The Coso Volcanic Field to the north contributes geothermal influences that can modulate swarm behavior through fluid migration along fractures. Historical records indicate persistent swarm activity in this locale. Since 2000, 71 swarms have been documented, with notable increases in frequency during certain years: 2004 recorded 7, 2010 recorded 7, and 2019 alone accounted for 21. These episodes typically involve clustered, low-magnitude events over days to weeks, reflecting the region's capacity for episodic strain release without producing large mainshocks. Swarm S20191011.1 initiated at 17:01 on 10 October 2019 and concluded at 12:00 on 15 October 2019, centered 16 km east-southeast of Little Lake. Over 114 hours and 58 minutes, the sequence produced 165 earthquakes. Analysis of the first 100 events reveals predominantly microseismic activity, with magnitudes ranging from -0.2 to 2.2. Depths clustered between 1 km and 11 km, though isolated events reached 14 km, suggesting activation across a vertically extensive fault network. Early events on 10 October showed moderate depths around 7-11 km, while subsequent activity on 11-13 October included shallower occurrences near 1-5 km, indicating possible upward migration of seismicity consistent with fluid-driven processes. Temporal distribution displayed bursts, such as multiple events within minutes on 11 October, followed by steadier rates. The largest event in the initial cohort reached magnitude 2.2 at 5 km depth. Overall, the swarm exhibited typical characteristics of the area, where cumulative energy release remains modest yet provides insights into fault connectivity and stress conditions. Such sequences underscore the importance of continuous monitoring in this shear zone for assessing evolving seismic hazards and potential links to nearby geothermal systems.
References
USGS Earthquake Catalog California Geological Survey Regional Reports SeismoSight Internal Swarm Classification Database