Seismic Swarm S20220714.1: Analysis of Activity Near Borrego Springs, California

The region 8 km NNE of Borrego Springs, California, lies within the tectonically active Peninsular Ranges province. This area experiences frequent seismic events due to its position along the San Jacinto Fault Zone, a major right-lateral strike-slip system within the broader San Andreas Fault network. The local geology features a complex arrangement of faults cutting through crystalline basement rocks and sedimentary basins, contributing to elevated seismicity rates.

Swarm S20220714.1 began at 09:03 on 13 July 2022 and concluded at 21:35 on 14 July 2022. Over 36 hours and 31 minutes, the sequence produced 26 earthquakes. The events clustered at depths primarily between 6 km and 11 km, with the majority occurring near 10–11 km. Magnitudes remained low overall, peaking at 3.2 for a single event at 16:01:36 on 13 July. Subsequent activity consisted of microearthquakes between 0.4 and 1.8 in magnitude, distributed across both days with the highest rate in the hours immediately following the largest shock.

This pattern aligns with typical swarm behavior in the region, where sequences of small events occur without a clear mainshock-aftershock progression. Depths indicate activity within the seismogenic zone of the local fault network, consistent with historical observations in the Anza-Borrego area.

Historical records since 1 January 2000 document 39 swarms in the same locale. Yearly counts include one swarm in 2001, two in 2002, one in 2003, two in 2005, two in 2009, six in 2010, three in 2011, three in 2012, four in 2013, one in 2014, two in 2015, four in 2016, two in 2017, one in 2018, three in 2020, and two in 2022. These statistics underscore the recurrent nature of swarm activity driven by the underlying fault architecture.

References

SeismoSight internal classification data for swarm S20220714.1.
USGS Earthquake Catalog for regional fault context.