Seismic Swarm S20220510.1: Analysis of Activity Near Ocotillo Wells, California

A seismic swarm designated S20220510.1 occurred 23 km west-southwest of Ocotillo Wells in San Diego County, California. The sequence began at 18:25 UTC on 9 May 2022 and concluded at 08:25 UTC on 10 May 2022, lasting 13 hours and 59 minutes. During this period, 26 earthquakes were recorded, with magnitudes between 0.9 and 3.5 and focal depths consistently between 10 and 13 km.

The events clustered tightly in both time and space. The largest shock, magnitude 3.5, struck at 21:35:33 UTC on 9 May at 11 km depth. It was followed within minutes by several events of magnitude 1.9 and 2.5. Subsequent activity consisted primarily of smaller shocks below magnitude 2.0, distributed across the remaining hours until the final event of magnitude 1.1 at 08:25:31 UTC on 10 May.

This swarm fits the established pattern of seismic activity in the region. Since 1 January 2000, seven prior swarms have been documented in the same area, occurring in 2007 (one swarm), 2009 (three swarms), 2010 (two swarms), and 2017 (one swarm). Such episodic clusters reflect the tectonic regime of the western Salton Trough, where distributed strike-slip faulting accommodates Pacific–North American plate motion.

The Ocotillo Wells area lies within the Anza-Borrego Desert, part of the broader San Andreas transform boundary. Crustal deformation here is accommodated along the San Jacinto Fault Zone and subsidiary structures such as the Coyote Creek Fault. Seismicity is typically shallow, occurring within the upper 15 km of the crust, consistent with the 10–13 km depths observed in this swarm. The region experiences frequent small-magnitude events due to its position at a right-stepping bend in the fault system, which promotes both mainshock–aftershock sequences and swarm-like behavior.

No damage or felt reports of significance were associated with the 3.5-magnitude event, as is typical for low-magnitude sequences in this sparsely populated desert setting. Continued monitoring by regional seismic networks remains essential for tracking whether future swarms evolve into larger triggered events along nearby fault strands.

References

USGS Earthquake Catalog
California Geological Survey Fault Activity Map
Southern California Seismic Network bulletins