Seismic Swarm VS20100123.1: Analysis of Activity Near Calipatria, California

A notable earthquake swarm, designated VS20100123.1, occurred 13 km west-northwest of Calipatria in Imperial County, California. The sequence began at 17:08 on 22 January 2010 and concluded at 20:12 on 24 January 2010, spanning 51 hours and 4 minutes. During this period, 46 earthquakes were recorded, with events clustered primarily on 23 January.

The swarm exhibited typical characteristics of low-to-moderate magnitude activity. Magnitudes ranged from 0.3 to 3.0, with the largest event reaching 3.0 at a depth of 2 km on 23 January at 13:17:17. Most events registered below magnitude 2.0, and depths were shallow, predominantly between 0 and 5 km. Activity showed two main phases: an initial small cluster on 22 January followed by a more intense burst on 23 January between 13:08 and 13:51, accounting for the majority of events. Later events on 23 and 24 January were sparse and of lower magnitude.

This swarm aligns with the tectonic environment of the Salton Trough, a pull-apart basin formed by the interaction of the San Andreas Fault system and the Imperial Fault. The region experiences frequent swarm activity due to its location within a transtensional regime involving right-lateral strike-slip faults and geothermal influences from underlying magmatic processes. Depths in the 0–5 km range are consistent with shallow crustal faulting common in this area.

Historical data indicate that 28 swarms have occurred in the region since 2000. Annual counts include one each in 2000, 2001, 2002, and 2004; four in 2003; three in 2005; five in 2008; eleven in 2009; and one in 2010 up to the date of this event. Such recurrent swarms reflect ongoing strain accommodation along regional faults without a single dominant mainshock.

References

USGS Earthquake Hazards Program catalog data for Imperial County, California.
California Geological Survey reports on Salton Trough seismicity.
Peer-reviewed studies on Brawley Seismic Zone swarm patterns in the Journal of Geophysical Research.