Seismic Swarm VS20091124.1: Analysis of Activity Near Niland, California
Seismic swarm VS20091124.1 occurred in the Imperial Valley region of southern California, centered 10 km southwest of Niland. The sequence began at 12:43 on 23 November 2009 and concluded at 15:52 on 27 November 2009, spanning 99 hours and 8 minutes. During this period, 69 earthquakes were recorded, with magnitudes ranging from 0.2 to 1.8 and focal depths between 0 and 7 km. The majority of events were shallow, with many occurring at depths of 0–3 km, indicating activity within the upper crustal layers typical of this tectonically active area.
The swarm exhibited classic characteristics of clustered seismicity, with peak activity on 24 November featuring multiple events per hour. Notable larger events included a magnitude 1.8 quake at 11:00 on 24 November at 2 km depth and several magnitude 1.4 events distributed across the sequence. Such swarms often lack a single dominant mainshock and instead reflect distributed stress release along fault networks.
The Niland area lies within the Salton Trough, a pull-apart basin formed by the interaction of the San Andreas Fault system and the Imperial Fault. This region experiences elevated seismicity due to right-lateral strike-slip faulting and geothermal activity associated with the underlying magmatic and hydrothermal systems beneath the Salton Sea. Historical records indicate persistent swarm activity linked to fluid migration and tectonic strain accumulation in the Brawley Seismic Zone.
Since 1 January 2000, 25 swarms have been documented in the vicinity. Yearly occurrences include one each in 2000, 2001, 2002, and 2004; three in 2003 and 2005; five in 2008; and ten in 2009. This pattern underscores the recurrent nature of swarm sequences in the Imperial Valley, driven by the region's high geothermal gradient and complex fault interactions.
Overall, swarm VS20091124.1 represents a typical low-magnitude episode in an area prone to such events, providing data for monitoring crustal deformation and geothermal processes.
References
USGS Earthquake Catalog (historical swarm data cross-verified for regional context)
California Geological Survey reports on Imperial Valley tectonics