Seismic Swarm S20160810.2 East of Big Pine, California

On 10 August 2016, a seismic swarm designated S20160810.2 was recorded 61 km east of Big Pine, California. The sequence began at 14:37 UTC and concluded at 19:56 UTC, encompassing 33 earthquakes over 5 hours and 19 minutes. Magnitudes ranged from 0.4 to 2.0, with the largest event occurring at 16:28:34 UTC. Focal depths were predominantly between 4 km and 10 km, though several events registered at shallower or anomalous depths. The swarm exhibited typical characteristics of clustered microseismicity, with events distributed across a compact area. Early activity featured smaller magnitudes clustered around 6–9 km depth, followed by a gradual increase in event frequency and a peak magnitude of 2.0. Later events maintained similar depth ranges, indicating a stable source volume without significant migration. This sequence represents the fourth swarm in the region since 1 January 2000. Prior swarms occurred in 2004, 2005, and 2010, each consisting of a single recorded cluster. Such episodic activity underscores the intermittent nature of strain release along local fault structures. The location lies within the Owens Valley region of eastern California, part of the Basin and Range Province. This area experiences active east-west extension driven by Pacific-North American plate interaction and westward escape of the Sierra Nevada block. The Owens Valley Fault Zone, responsible for the great 1872 earthquake, traverses the valley and accommodates significant right-lateral strike-slip motion alongside normal faulting. Seismicity east of Big Pine aligns with subsidiary faults and fracture networks that respond to regional tectonic stress. Historical records document recurrent moderate-to-large earthquakes in Owens Valley, reflecting long-term strain accumulation. Modern instrumental monitoring reveals that swarms like S20160810.2 contribute to background seismicity without immediate indication of larger rupture potential. Depths observed in the swarm are consistent with brittle failure in the upper crust of this extensional regime. Continued surveillance by regional seismic networks remains essential for distinguishing swarm behavior from foreshock sequences. The 2016 event adds to the catalog of low-magnitude clusters that characterize deformation in this tectonically active corridor.

References

SeismoSight internal swarm classification records
USGS Earthquake Catalog (Owens Valley regional tectonics)
California Geological Survey fault database