An intense earthquake swarm started near Salton Sea, California on September 30, 2020, with 421 earthquakes detected by 07:00 UTC on October 1.
- The swarm is centered just southeast of Salton Sea, near Westmorland in Imperial Valley, in an area with a history of intense swarms. The most notable earthquakes in the region include M5.8 in 1981 and M5.4 in 2012.
- During this earthquake swarm, the probability of larger earthquakes in this region is significantly greater than usual, the USGS said.
- The swarm is taking place in Brawley Seismic Zone, a network of small faults that connect the San Andreas and Imperial faults.