Seismic Swarm S20100424.1: Activity Near Coso Junction, California

Seismic swarm S20100424.1 occurred in the Coso region of eastern California, centered 10 km east-southeast of Coso Junction. The sequence began at 11:32 on 23 April 2010 and concluded at 03:17 on 26 April 2010, spanning 63 hours and 44 minutes. During this interval, 41 earthquakes were recorded.

The events were characterized by low to moderate magnitudes, with the largest reaching 2.7. Most events registered below magnitude 2.0, and focal depths remained shallow, predominantly between 0 and 3 km. A small number of events extended to 7–10 km. The temporal distribution showed initial clustering on 23 April, followed by sustained low-level activity through 25 April and a final event early on 26 April.

This swarm aligns with the established seismicity patterns of the Coso Volcanic Field. The area lies within the eastern California shear zone, where northwest-trending right-lateral strike-slip faults interact with localized volcanic and geothermal systems. Shallow seismicity frequently reflects fluid migration or minor magmatic processes beneath the rhyolite domes and geothermal reservoirs.

Historical records indicate 28 swarms in the region since 2000. Yearly counts include four in 2000, four in 2001, two in 2002, seven in 2004, two in 2005, six in 2006, one in 2009, and two in 2010. Such episodic swarms are typical and rarely produce significant ground shaking or damage given their modest magnitudes and limited depths.

The Coso Volcanic Field hosts one of California’s largest geothermal power plants, underscoring the link between tectonic stress, hydrothermal circulation, and observed seismicity. Continuous monitoring by regional networks supports ongoing assessment of swarm characteristics for hazard evaluation.

References

SeismoSight internal swarm classification S20100424.1
USGS Earthquake Hazards Program regional seismicity reports
California Geological Survey, Coso Volcanic Field overview