Seismic Swarm S20251117.1: Analysis of Activity Near Borrego Springs, California
Seismic swarm S20251117.1 occurred approximately 24 km NNW of Borrego Springs in San Diego County, California. The sequence initiated at 08:22 on 16 November 2025 and concluded at 01:16 on 20 November 2025, spanning 88 hours and 54 minutes. During this interval, 56 earthquakes were recorded.
The events exhibited predominantly low magnitudes, with the largest reaching 2.9. Depths remained shallow, generally between 1 km and 15 km, consistent with the region's upper crustal dynamics. Activity clustered most intensely during the first 24 hours, featuring multiple events above magnitude 1.0, followed by a gradual decline in both frequency and size. Representative events include the initial 2.5-magnitude shock at 2 km depth on 16 November at 08:22, a 2.9-magnitude event at 3 km on 17 November at 00:10, and several smaller aftershocks registering between 0.2 and 1.7 through 20 November.
This swarm reflects typical behavior along the San Jacinto Fault Zone, a right-lateral strike-slip system that accommodates a significant portion of the Pacific-North American plate boundary motion. The zone lies adjacent to the San Andreas Fault and has produced numerous historical earthquakes, including magnitude 6+ events in the 20th century. Shallow seismicity in this area often manifests as swarms due to fluid migration and stress transfer within fractured crystalline basement rocks of the Peninsular Ranges.
Since 2000, the Borrego Springs vicinity has experienced 46 documented swarms, with notable concentrations in 2010 (five events), 2016 (four events), and 2022 (seven events). These recurrent episodes underscore the ongoing tectonic loading in Southern California, where annual slip rates on the San Jacinto Fault average 10–15 mm per year. No damage or felt reports above moderate intensity were associated with S20251117.1, aligning with the low-energy release observed.
References
- United States Geological Survey Earthquake Catalog
- California Geological Survey Fault Activity Map
- Southern California Earthquake Data Center Swarm Database