Seismic Swarm VS20161031.1 Southwest of Niland, California
The seismic swarm VS20161031.1 occurred 6 km southwest of Niland, California, beginning at 09:00 on 31 October 2016 and ending at 08:50 on 1 November 2016. In 23 hours and 50 minutes, the sequence produced 39 earthquakes. Magnitudes ranged from 1.2 to 3.4, with the largest event reaching 3.4 at a depth of 3 km shortly after 10:40 on 31 October. Most events clustered at depths of 2–4 km, consistent with shallow crustal processes common in this portion of the Imperial Valley.
The Niland area lies within the Salton Trough, a tectonically active pull-apart basin formed by right-lateral shear between the San Andreas and Imperial fault systems. The trough marks the transition from the San Andreas Fault to the Imperial Fault and hosts the Brawley Seismic Zone, where frequent earthquake swarms occur alongside geothermal activity driven by high heat flow and fluid migration. These conditions produce shallow seismicity often linked to both tectonic strain and hydrothermal processes.
Historical records show 71 swarms in the region since 1 January 2000. Annual counts varied, with notable peaks of 13 swarms each in 2010 and 2013, followed by lower activity in 2014 and 2015 before two swarms in 2016. The 2016 sequence VS20161031.1 fits this established pattern of episodic swarm activity.
The temporal distribution of the 39 events showed an initial burst of larger-magnitude shocks within the first two hours, followed by a gradual decline. Depths remained consistently shallow, reinforcing the interpretation of fluid-influenced or geothermal-related triggering typical of the Salton Trough.
References
SeismoSight internal swarm classification VS20161031.1
USGS Earthquake Catalog for Imperial Valley, California
California Geological Survey, Salton Trough tectonic summary