Seismic Swarm S20120209.1 Near Niland, California
Seismic swarm S20120209.1 occurred approximately 6 km west-northwest of Niland in Imperial County, California. The sequence began at 16:25 on 8 February 2012 and concluded at 17:20 on 10 February 2012, spanning 48 hours and 54 minutes. During this interval, 29 earthquakes were recorded, with magnitudes ranging from 0.3 to 2.5 and focal depths primarily between 0 and 5 km.
The swarm exhibited typical characteristics of clustered microseismicity, featuring a rapid onset followed by a gradual decline in activity. The largest event reached magnitude 2.5 at 09:34 on 9 February at a depth of 0 km. Multiple events clustered around 22:00–23:00 on 8 February and 06:00–12:00 on 9 February, reflecting episodic energy release. Depths remained shallow throughout, consistent with activity in the uppermost crust.
Niland lies within the Imperial Valley, a tectonically active region at the southern terminus of the San Andreas Fault system. The area forms part of the Brawley Seismic Zone, where right-lateral strike-slip faulting accommodates Pacific-North American plate motion. Geothermal fields and volcanic features, including the Salton Buttes, indicate ongoing crustal extension and magmatic influence that promote swarm-type seismicity rather than large mainshock-aftershock sequences.
Historical records document 42 swarms in the region since 1 January 2000. Annual counts show variability, with notable increases in 2009 (11 swarms) and 2010 (13 swarms). Earlier years recorded fewer events, including single swarms in 2000, 2001, 2002, and 2004. This pattern underscores the recurrent nature of swarm activity driven by fluid migration and fault-zone heterogeneity in the Imperial Valley.
The 2012 swarm aligns with the area's established seismic behavior. Shallow depths and low magnitudes suggest limited rupture dimensions, typical of induced or fluid-driven sequences in this geothermal setting. No damage or felt reports beyond minor shaking were associated with the events.
References
- United States Geological Survey Earthquake Catalog
- California Geological Survey Regional Fault and Seismicity Reports
- SeismoSight internal swarm classification records