Seismic Swarm VS20101228.1: Analysis of Activity Near Niland, California
A notable earthquake swarm, designated VS20101228.1, occurred 10 km west-southwest of Niland, California, in the Imperial Valley. The sequence began at 23:41 UTC on 27 December 2010 and concluded at 11:10 UTC on 28 December 2010, spanning 11 hours and 28 minutes. During this period, 66 earthquakes were recorded, with magnitudes ranging from 0.3 to 3.7 and focal depths primarily between 0 and 5 km.
The swarm exhibited a typical pattern of clustered, low-to-moderate magnitude events without a dominant mainshock. Early activity included events of magnitude 1.1 and 1.0 within the first few minutes, followed by a gradual increase in frequency and intensity. Peak activity featured a magnitude 3.7 earthquake at 02:38 UTC on 28 December at 4 km depth, accompanied by several events exceeding magnitude 2.0, including 2.3, 2.1, and 3.5. Subsequent events tapered off, with smaller magnitudes dominating the later hours. Depths remained shallow throughout, consistent with activity in the brittle upper crust of the region.
This swarm aligns with the broader seismicity of the Imperial Valley, situated within the Salton Trough—a tectonically active pull-apart basin formed by the interaction of the San Andreas and San Jacinto fault systems. The area experiences frequent earthquake swarms due to right-lateral strike-slip faulting and associated geothermal processes linked to the nearby Salton Sea. Shallow depths and swarm behavior reflect fluid migration and stress transfer along minor faults rather than large-scale rupture on major strands.
Historical data indicate persistent swarm activity in the region. Since 1 January 2000, 38 swarms have been documented, with notable yearly distributions: one each in 2000, 2001, 2002, and 2004; four in 2003; three in 2005; five in 2008; eleven in 2009; and eleven in 2010. This recurrence underscores the Imperial Valley's role as a high-strain zone prone to episodic clustered seismicity, often influenced by regional tectonic loading and hydrothermal activity.
Such swarms provide valuable insights into fault mechanics and seismic hazard assessment. Monitoring sequences like VS20101228.1 aids in distinguishing swarm behavior from foreshock-mainshock-aftershock patterns, supporting refined models of crustal deformation in transform boundary settings.
References
- SeismoSight internal swarm classification records for VS20101228.1.
- United States Geological Survey (USGS) Earthquake Hazards Program documentation on Imperial Valley tectonics.