Seismic Swarm S20220113.1 Near Borrego Springs, California

An earthquake swarm designated S20220113.1 was recorded 13 km north of Borrego Springs, California, beginning at 03:02 UTC on 13 January 2022 and concluding at 08:58 UTC on 17 January 2022. The sequence lasted 101 hours and 56 minutes and included 157 earthquakes. This event occurred within the tectonically active San Jacinto Fault Zone, a major component of the Pacific-North American plate boundary.

Analysis of the first 100 events reveals predominantly low-magnitude activity. Magnitudes ranged from 0.1 to 3.8, with the largest shock measuring 3.8 at a depth of 13 km occurring shortly after the swarm onset. Most events clustered between magnitudes 0.5 and 1.5. Depths were concentrated between 12 and 15 km, indicating activity within the mid-crustal section of the fault zone. A secondary peak of 2.7 magnitude was noted later on 13 January at shallower depth. The temporal distribution showed the highest frequency in the initial hours, followed by a gradual decline, consistent with swarm behavior rather than a classic mainshock-aftershock sequence.

The Borrego Springs region lies in the Anza-Borrego Desert, where the San Jacinto Fault Zone accommodates a significant portion of the relative plate motion. This strike-slip system features multiple strands, including the Coyote Creek Fault, that produce both large earthquakes and frequent swarm activity due to fluid migration and aseismic slip processes. Historical records indicate the area has experienced repeated seismic swarms, reflecting ongoing strain accumulation and release along these structures.

Since 2000, 53 swarms have been documented in the vicinity. Annual counts include one swarm each in 2001, 2003, 2019, and 2021; two each in 2002, 2005, 2009, 2014, and 2015; three each in 2011 and 2012; four each in 2013 and 2016; five each in 2010 and 2017; six in 2018; and nine in 2020. This pattern underscores the persistent seismic restlessness of the San Jacinto Fault Zone compared with other segments of the broader San Andreas system.

Such swarms provide valuable data on fault mechanics in Southern California. Monitoring by regional seismic networks continues to track activity in this area, contributing to improved hazard assessments for nearby communities and infrastructure. Ongoing research integrates swarm statistics with geodetic measurements to refine models of fault behavior and earthquake potential.

References

• SeismoSight internal swarm classification data
• USGS Earthquake Catalog for regional seismicity records