Seismic Swarm S20020907.1 near Coso Junction, California

SeismoSight recorded earthquake swarm S20020907.1 beginning at 16:00 on 6 September 2002 and concluding at 17:25 on 8 September 2002. The sequence occurred 7 km northeast of Coso Junction, California, and comprised 31 events over 49 hours and 25 minutes.

Events displayed predominantly low magnitudes, with the largest reaching 3.5 at 00:02 on 7 September at a depth of 2 km. Most events registered below magnitude 1.5 and occurred at shallow depths between 0 and 4 km, although one event was noted at 11 km. Activity peaked during the early hours of 7 September before tapering through 8 September.

This swarm reflects typical behavior in the Coso region, where clusters of small earthquakes often arise from fluid migration within fractured volcanic and geothermal systems rather than from a single large tectonic rupture. Depths concentrated near the surface align with known hydrothermal pathways that facilitate rapid stress adjustments.

Since 1 January 2000, nine swarms have been documented in the immediate area. Earlier episodes included four swarms in 2000 and four in 2001, indicating recurrent seismic unrest prior to the 2002 sequence.

The Coso Junction area lies within the western Basin and Range province of eastern California, where extensional tectonics interact with the Coso Volcanic Field. This field has produced rhyolitic and basaltic eruptions over the past several million years, with the most recent activity in the Holocene. The landscape features active geothermal fields, hot springs, and fault zones that accommodate both tectonic strain and magmatic heat flow. Ongoing geothermal energy production in the vicinity further influences local seismicity patterns through fluid extraction and injection.

Seismic monitoring continues to track such swarms as indicators of subsurface processes. The 2002 sequence remains a representative example of the persistent low-level activity that characterizes this geothermally and volcanically active terrain.

References
SeismoSight internal swarm catalog S20020907.1
USGS Earthquake Catalog (Coso region, 2000–2002)
California Geological Survey, Coso Volcanic Field summary