A significant earthquake swarm is unfolding in southern California, impacting the area around the Salton Sea east of San Diego, south of Palm Springs, and southeast of Los Angeles. 47 earthquakes with a magnitude of 2.5 or greater have struck the area, with the strongest being a 5.3 which struck at 10:55am local time today.
The strong 5.3 earthquake struck about 6 and a half miles west of Calipatria at a depth of 3.6 miles. More than 700 residents from Los Angeles to San Diego to El Centro reported experiencing the quake to the USGS, including many that reported “strong shaking.”
Today’s significant earthquake swarm is occurring near the Salton Sea, a shallow landlocked lake with a high salt concentration in Riverside and Imperial counties of California. The Salton Sea sits on the San Andreas Fault at the southern end of the state of California. In this region, the Earth’s crust is being stretched. Today’s earthquakes are tied to submerged faults near the southern end of the San Andreas Fault. Called the Brawley seismic zone, this extensional region connects the San Andreas with the Imperial Fault in southern California.
Today’s swarm comes on the heels of another earthquake swarm that impacted the Disney Land area last weekend north of today’s swarm.
An earthquake swarm, according to the USGS, is a sequence of mostly small earthquakes with no identifiable mainshock. Swarms are usually short-lived, but they can continue for days, weeks, or sometimes even months. They often recur at the same locations. Most swarms are associated with geothermal activity. Swarms are usually not tied to aftershocks. Aftershocks are a sequence of earthquakes that happen after a larger mainshock on a fault. Aftershocks occur near the fault zone where the mainshock rupture occurred and are part of the “readjustment process” after the main slip on the fault. Aftershocks become less frequent with time, although they can continue for days, weeks, months, or even years for a very large mainshock.
California is home to the border between the North American and Pacific tectonic plates, and this plate boundary area is normally rich with seismic activity. The San Andreas fault is the state’s longest fault, considered by experts as the most dangerous too.
A big earthquake is likely, although the exact timing for when isn’t exactly known yet, according to USGS scientists. USGS regional scenarios anticipate 1,800 deaths and 50,000 injuries in the event of a major San Andreas earthquake. More than 3 million homes could be damaged, at a reconstruction cost of $289 billion. It is not known if today’s swarm is a precursor to a larger seismic event.