Seismic Swarm S20190118.1 Near Calipatria, California

Seismic swarm S20190118.1 occurred approximately 10 km west-northwest of Calipatria in Imperial County, California, within the tectonically active Salton Trough. The sequence began at 12:26 on 17 January 2019 and concluded at 01:42 on 22 January 2019, spanning 109 hours and 15 minutes. During this interval, 71 earthquakes were recorded, with magnitudes ranging from 0.6 to 3.3 and focal depths primarily between 5 and 18 km.

The Salton Trough forms a sediment-filled pull-apart basin at the southern terminus of the San Andreas Fault system, where right-lateral strike-slip motion transitions into the extensional regime of the Gulf of California. This setting produces elevated geothermal gradients and frequent microseismicity. The Imperial Valley, encompassing Calipatria, lies near the Brawley Seismic Zone and the Imperial Fault, both of which accommodate significant strain through distributed faulting and fluid-driven processes. Earthquake swarms in this region commonly arise from aseismic slip, pore-pressure changes, or magma-related intrusions rather than a single mainshock-aftershock sequence.

Event timing showed clustering on 18 January, including the largest shock of magnitude 3.3 at 08:19. Subsequent activity tapered gradually, with smaller events persisting through 21 January. Depths remained shallow to intermediate, consistent with the brittle upper crust overlying ductile zones influenced by high heat flow from underlying magmatic and hydrothermal systems. Such patterns align with historical observations of swarm behavior in the Imperial Valley, where sequences often last days to weeks and involve dozens of events without a dominant rupture.

Since 2000, the area has hosted 76 documented swarms, with notable concentrations in 2009 (11 events), 2010 (13), 2012 (11), and 2013 (13). These episodes underscore the persistent seismic productivity of the Salton Trough, driven by ongoing plate-boundary deformation. Monitoring by regional networks provides critical data for assessing hazards to nearby infrastructure, including geothermal facilities and agricultural zones.

References

USGS Earthquake Catalog
Southern California Seismic Network reports
California Geological Survey regional tectonic summaries