Seismic Swarm S20101024.1 Near Coso Junction, California
A notable earthquake swarm, designated S20101024.1, occurred in the Coso region of California from 16:40 on 23 October 2010 to 21:59 on 30 October 2010. Over 173 hours and 19 minutes, the swarm produced 92 earthquakes. The epicenters were located approximately 16 km east of Coso Junction.
The sequence began with low-magnitude events on 23 October, including shocks of magnitude 0.4, 0.2, and 0.0 at depths of 1–2 km. Activity intensified on 24 October, featuring a magnitude 2.9 event at 7 km depth at 08:31, followed by multiple events between magnitudes 0.4 and 2.5, predominantly at depths of 7–9 km. Subsequent days showed continued but generally smaller events, with occasional peaks such as magnitude 1.9 on 26 October and magnitudes 2.6 and 2.7 on 29 October. Depths remained shallow throughout, mostly between 0 and 9 km, consistent with the area’s known seismogenic zone. The swarm concluded with a magnitude 1.3 event at 6 km depth on 30 October.
This swarm aligns with the tectonic setting of the Coso Volcanic Field, situated in the western Basin and Range province. The field encompasses Pleistocene rhyolite domes, basaltic lava flows, and an active geothermal system driven by shallow crustal heat sources. Regional extension along normal faults, combined with possible magmatic or hydrothermal fluid migration, frequently triggers earthquake swarms rather than mainshock-aftershock sequences. Depths in the 0–10 km range reflect brittle failure above the ductile transition zone influenced by elevated geothermal gradients.
Historical records indicate 29 swarms in the same area since 1 January 2000, distributed across years as follows: four in 2000, four in 2001, two in 2002, seven in 2004, one in 2005, six in 2006, one in 2009, and four in 2010. These recurrent swarms underscore the persistent seismic and volcanic character of the Coso region.
- USGS Earthquake Catalog
- California Geological Survey regional reports
- Coso Volcanic Field geothermal studies (USGS Professional Papers)