Analysis of Earthquake Swarm VS20130603.1 Near Niland, California

Earthquake swarm VS20130603.1 occurred 9 km west of Niland in Imperial County, California, within the tectonically active Imperial Valley. This region lies at the southern terminus of the San Andreas Fault system, where the Pacific and North American plates interact along a network of strike-slip and normal faults associated with the Brawley Seismic Zone and the Salton Trough. The area experiences frequent seismic activity due to right-lateral shear and crustal extension linked to the transition between the San Andreas Fault and the Gulf of California spreading center.

The swarm initiated at 08:54 on 3 June 2013 and concluded at 00:49 on 7 June 2013, spanning 87 hours and 54 minutes. During this period, 134 earthquakes were recorded. Depths of the events remained shallow, predominantly between 0 and 5 km, consistent with the brittle upper crust in this geothermal-influenced basin. Magnitudes ranged from 0.2 to 3.9, with the largest event (M3.9) occurring at 19:04 on 3 June at a depth of 2 km. Subsequent notable shocks included an M3.5 at 19:46 on 4 June and multiple M3.0 events.

Examination of the first 100 events reveals temporal clustering, with the highest activity concentrated in the initial 36 hours. Early events on 3 June showed a rapid succession of magnitudes between 0.5 and 3.9, followed by sustained lower-magnitude sequences into 4 and 5 June. Depths exhibited minor variation but stayed consistently shallow, suggesting fluid migration or aseismic slip as possible driving mechanisms in this rift-related setting. No events exceeded magnitude 4.0, aligning with the swarm's characteristic lack of a dominant mainshock.

The Imperial Valley has a well-documented history of earthquake swarms driven by its position in an extensional tectonic regime. Geothermal fields near the Salton Sea further contribute to swarm occurrence through hydrothermal fluid movement along faults. Since 2000, the broader region has recorded 59 swarms, with annual counts varying from one in 2000 to peaks of 13 in 2010. This pattern underscores the ongoing seismic productivity of the area, where swarms often reflect episodic strain release rather than singular large ruptures.

Updated geological assessments confirm that the Niland vicinity remains susceptible to such sequences owing to its proximity to the San Andreas Fault and subsidiary structures. Monitoring by regional networks continues to track these events to better understand precursory signals and mitigate hazards in this populated agricultural and geothermal zone.

References

United States Geological Survey Earthquake Catalog California Geological Survey Regional Fault Maps Southern California Seismic Network Swarm Reports