Seismic Swarm S20100114.1: Analysis of Activity Near Coso Junction, California

The Coso region in eastern California lies within the tectonically active Basin and Range province, where extensional faulting interacts with the Coso Volcanic Field. This Quaternary volcanic center features rhyolitic domes, basaltic flows, and an active geothermal system that supports commercial power production. Seismicity in the area frequently manifests as swarms driven by hydrothermal fluid migration and minor magmatic processes rather than large tectonic events. Swarm S20100114.1 began at 18:05 UTC on 13 January 2010 and concluded at 02:43 UTC on 25 January 2010. The sequence was centered approximately 10 km east of Coso Junction and produced 443 events over 272 hours and 38 minutes. Examination of the first 100 recorded earthquakes reveals predominantly shallow focal depths, with most events occurring between 0 and 3 km. Magnitudes remained modest, peaking at 4.4, while many events clustered below magnitude 1.0. Temporal patterns show distinct bursts of activity, including a notable concentration of higher-magnitude events around midday on 14 January and another intense cluster late on 15 January that included multiple events above magnitude 2.0 within minutes. Depth distribution indicates a concentration near the surface, consistent with fluid-driven fracturing in the geothermal reservoir. Negative depth values in a small number of solutions likely reflect location uncertainty rather than true above-sea-level sources. The progression from isolated low-magnitude events on 13 January to more energetic sequences on subsequent days suggests episodic pressure changes within the hydrothermal system. Historical records document 26 seismic swarms in the Coso area since 1 January 2000. Yearly counts include four swarms each in 2000 and 2001, two in 2002, seven in 2004, two in 2005, six in 2006, and one in 2009. This recurring pattern underscores the persistent volcanic and geothermal influence on local seismicity. The 2010 swarm fits within this established framework, highlighting the value of continuous monitoring for distinguishing routine geothermal unrest from any escalation that might warrant heightened attention.

References

• United States Geological Survey Earthquake Catalog
• California Geological Survey regional reports on the Coso Volcanic Field