Seismic Swarm S20200322.1 Near Searles Valley, California
Seismic swarm S20200322.1 was recorded in the Searles Valley region of California, beginning at 13:59 on 21 March 2020 and concluding at 03:58 on 1 April 2020. The events were centered 11 km southwest of Searles Valley, within the tectonically active Eastern California Shear Zone. Over 253 hours and 58 minutes, the swarm produced 140 earthquakes.
Analysis of the first 100 events reveals predominantly low-magnitude activity. Initial shocks included a magnitude 0.8 event at 6 km depth, followed by magnitudes ranging from 0.0 to 2.5. The strongest event reached magnitude 2.5 at 7 km depth on 22 March. Depths varied between 0 km and 14 km, with most clustered between 5 km and 10 km, consistent with shallow crustal faulting in the area. Later events in the sequence maintained similar characteristics, showing no escalation to higher magnitudes within the sampled period.
The swarm occurred in a region with a documented history of seismic swarms. Since 1 January 2000, 51 swarms have been identified in the vicinity. Yearly distribution includes single swarms in 2010, 2011, 2012, 2013, 2015, and 2016, followed by a marked increase with 35 swarms in 2019 and 10 in 2020. This pattern aligns with the broader tectonic setting of the Mojave Desert, where distributed strike-slip faults accommodate Pacific-North American plate motion.
A notable prior event was the magnitude 7.1 Ridgecrest earthquake on 6 July 2019, located 6 km from the swarm center. This mainshock formed part of the Ridgecrest Earthquake Sequence and highlighted the area's potential for significant seismic release along nearby fault networks.
Geologically, Searles Valley lies within the Basin and Range Province, characterized by extensional tectonics and northwest-trending right-lateral faults. The local crust experiences ongoing deformation, with historical activity influenced by proximity to the San Andreas Fault system. Such conditions promote episodic swarm behavior rather than isolated large events.
References
- SeismoSight internal swarm classification data (S20200322.1 parameters and event list)
- USGS Earthquake Catalog for regional historical seismicity and Ridgecrest sequence details