Seismic Swarm S20100405.3 Near Bombay Beach, California
Seismic swarm S20100405.3 was recorded in the Imperial Valley region of Southern California. The sequence began at 04:48 on 4 April 2010 and concluded at 02:19 on 11 April 2010, spanning 165 hours and 30 minutes. A total of 132 earthquakes were detected, centered 12 km south-southeast of Bombay Beach. This location lies within the tectonically active Salton Trough, a pull-apart basin formed by the interaction of the San Andreas Fault system and the Imperial Fault.
The Salton Trough forms part of the boundary between the Pacific and North American plates. Right-lateral strike-slip motion along the San Andreas Fault transitions southward into a zone of distributed deformation that includes the Brawley Seismic Zone and the Imperial Fault. Shallow seismicity in this area is frequently linked to both tectonic strain release and geothermal fluid movement associated with the underlying magmatic system beneath the Salton Sea. Depths of events in swarm S20100405.3 remained predominantly between 0 and 9 km, consistent with the brittle upper crust in this extensional setting.
Analysis of the first 100 events shows a predominance of microearthquakes. Magnitudes ranged from 0.3 to 2.0, with the largest events reaching M2.0 on 5 April at 01:40 and 03:22. Depths clustered between 0 and 3 km for most events, although several reached 5–9 km. Temporal distribution indicates an initial burst of activity on 4 April, followed by sustained low-level seismicity through 7 April. No clear mainshock-aftershock pattern emerged; instead, the sequence exhibited the typical characteristics of an earthquake swarm driven by fluid migration or aseismic slip.
The Imperial Valley has a well-documented history of swarm activity. Since 2000, thirty swarms have been identified in the region. Annual counts show variability, with notable increases in 2003 (4 swarms), 2008 (5 swarms), and 2009 (11 swarms). Swarm S20100405.3 represents one of three recorded in 2010. These recurrent swarms reflect ongoing strain accumulation and release along the southern San Andreas Fault and adjacent structures, where creep and triggered slip are common.
Such sequences contribute to the long-term seismic hazard assessment of the Coachella Valley and Imperial Valley. Although individual events in S20100405.3 were small, the cumulative energy release and spatial migration patterns provide data for models of fault interaction and fluid-driven seismicity in the Salton Trough.
References
SeismoSight internal swarm classification database USGS Earthquake Hazards Program regional tectonic summaries Southern California Earthquake Data Center historical catalogs