Seismic Swarm S20120229.1 Near Niland, California
Seismic swarm S20120229.1 occurred in the Imperial Valley of southern California, centered 4 km west-southwest of Niland. The sequence began at 14:48 UTC on 29 February 2012 and concluded at 05:39 UTC on 1 March 2012, spanning 14 hours and 51 minutes. During this interval, 34 earthquakes were recorded.
The swarm exhibited a typical pattern of clustered, low-to-moderate magnitude events without a single dominant mainshock. Magnitudes ranged from 0.3 to 3.3, with two events reaching the maximum magnitude of 3.3. Depths were predominantly shallow, concentrated between 0 and 7 km, consistent with activity in the uppermost crust. The initial event at 14:48 registered magnitude 3.3 at 1 km depth, followed shortly by a magnitude 3.1 event. Subsequent activity included multiple events above magnitude 2.0, interspersed with numerous smaller shocks below magnitude 1.5.
This sequence aligns with the tectonic environment of 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 ongoing right-lateral shear and extension associated with the Pacific-North America plate boundary. Geothermal fields and volcanic features linked to the spreading center beneath the Salton Sea contribute to elevated seismicity rates.
Historical records indicate frequent swarm activity in the area. Since 2000, 45 swarms have been documented, with notable concentrations in 2009 (11 swarms) and 2010 (13 swarms). Earlier years showed lower but consistent occurrences, including single swarms in 2000, 2001, 2002, and 2004. The 2012 swarm was one of three recorded that year.
Such swarms are characteristic of the Brawley Seismic Zone and surrounding Imperial Valley, where fluid migration and aseismic slip often accompany earthquake clusters. Shallow focal depths underscore the influence of local geothermal and hydrological processes on fault behavior.
The provided swarm parameters originate from internal SeismoSight classification records. Broader regional context draws from established geological understanding of the Imperial Valley.
References
- SeismoSight internal swarm classification database
- United States Geological Survey (USGS) earthquake catalog summaries for Imperial County, California
- California Geological Survey reports on Salton Trough tectonics