Seismic Swarm VS20131101.1: Analysis of Earthquake Activity Near Niland, California
Seismic swarm VS20131101.1 occurred 8 km southwest of Niland, California, in Imperial County. The sequence began at 17:31 on 31 October 2013 and concluded at 10:11 on 1 November 2013, spanning 16 hours and 39 minutes. During this period, 31 earthquakes were recorded, with magnitudes ranging from 0.2 to 2.3 and focal depths between 0 and 8 km.
The largest event reached magnitude 2.3 at a depth of 1 km shortly after midnight on 1 November. Most events remained below magnitude 1.5 and clustered at shallow depths, consistent with swarm behavior where energy release occurs through numerous small shocks rather than a single mainshock-aftershock sequence. Event timing showed initial activity on the evening of 31 October, followed by a cluster of events between 00:00 and 01:30 on 1 November, and a gradual decline toward the sequence end.
Niland lies within the Salton Trough, a tectonically active pull-apart basin formed by the interaction of the San Andreas Fault system and the Imperial Fault. The region experiences frequent microseismicity due to right-lateral strike-slip faulting and associated geothermal processes linked to the Salton Sea geothermal field. Shallow crustal depths in this area facilitate fluid migration that can trigger earthquake swarms through pore-pressure changes.
Historical records indicate 64 swarms in the region since 1 January 2000. Annual counts include one swarm each in 2000, 2001, 2002, and 2004; three swarms in 2003 and 2005; five in 2008; eleven in 2009; thirteen in 2010; four in 2011; eleven in 2012; and ten in 2013. These episodes reflect persistent tectonic strain accumulation and release along the Brawley Seismic Zone and adjacent faults.
Such swarms contribute to ongoing monitoring efforts by regional seismic networks, aiding assessment of potential escalation toward larger events. Continued observation supports hazard evaluation in this densely faulted landscape.
References
USGS Earthquake Hazards Program
California Geological Survey
Southern California Earthquake Data Center