Earthquake Swarm S20150217.1 Near Little Lake, California

An earthquake swarm designated S20150217.1 was recorded beginning at 19:25 on 16 February 2015 and concluding at 20:26 on 27 February 2015. The events were centered 33 km east-northeast of Little Lake, California. Over a period of 265 hours and 1 minute, the swarm comprised 139 earthquakes. Analysis of the first 100 events reveals predominantly low-magnitude activity. Magnitudes ranged from -0.2 to 2.6, with the majority falling between 0.5 and 1.3. Depths were consistently shallow, typically between 0 and 8 km, and many events registered at or near the surface. The sequence exhibited no dominant mainshock followed by decaying aftershocks; instead, events occurred in clusters without a clear temporal decay pattern, consistent with swarm behavior driven by fluid migration or aseismic slip along local faults. The region surrounding Little Lake lies within the Eastern California Shear Zone, a zone of distributed right-lateral shear accommodating part of the Pacific-North America plate motion. This tectonic setting features numerous northwest-trending strike-slip faults and is adjacent to the Coso Volcanic Field, where geothermal activity and magmatic processes contribute to elevated seismicity rates. Historical records document frequent earthquake swarms in the area, reflecting both tectonic strain accumulation and hydrothermal influences. Since 1 January 2000, 43 swarms have occurred in the vicinity. Annual counts include four in 2000, four in 2001, one in 2002, seven in 2004, one in 2005, six in 2006, one in 2008, one in 2009, seven in 2010, one in 2011, four in 2012, four in 2013, and two in 2014. These episodes underscore the persistent seismic character of the locale.

References

• SeismoSight internal swarm classification records
• USGS Earthquake Catalog (event locations and magnitudes)