Seismic Swarm S20100504.1 Near Ocotillo, California

The seismic swarm S20100504.1 occurred 5 km southwest of Ocotillo, California, within the tectonically active Imperial Valley. This region forms part of the Salton Trough, a pull-apart basin created by the right-lateral motion along the Pacific-North American plate boundary and associated strike-slip fault systems. Ongoing extension and fault interactions produce frequent microseismicity and occasional swarms in this area. The swarm began at 14:43 on 3 May 2010 and ended at 17:32 on 5 May 2010, lasting 50 hours and 49 minutes. A total of 89 earthquakes were recorded. Magnitudes ranged from 0.3 to 3.1, with the largest event (magnitude 3.1) occurring on 4 May at 18:24:32 at a depth of 6 km. Other notable events included magnitudes of 2.9, 2.6, 2.5, and multiple 2.4 events. Focal depths were predominantly between 2 km and 11 km, indicating shallow crustal activity typical of the local fault network. Event timing showed clustering, with elevated rates on 4 May between 10:00 and 20:00 and additional peaks on 5 May. Depths remained consistent across the sequence, suggesting a compact source volume without significant migration. Since 1 January 2000, ten swarms have been documented in the area. Earlier episodes occurred in 2006 (three swarms), 2007 (one swarm), 2009 (two swarms), and 2010 (four swarms, including the present event). This pattern reflects recurrent strain release along secondary faults in the Imperial Valley. The swarm provides insight into background seismicity levels and may relate to stress adjustments following larger regional events. Depths and magnitudes align with typical activity in the Coyote Mountains and adjacent fault zones.

References

SeismoSight internal swarm classification S20100504.1
USGS Earthquake Catalog (Imperial Valley, CA)
California Geological Survey regional fault maps