Over 300 Quakes, Mag 4.7, Hit Brawley Area

A swarm of more than 300 earthquakes, including one reaching magnitude 4.7, struck the Brawley area in Southern California's Imperial Valley over a 24-hour period starting Saturday afternoon, prompting heightened monitoring by emergency officials but causing no reported injuries or damage.

The United States Geological Survey recorded the initial quake, a magnitude 3.5 event, at around 4:14 p.m. local time about two miles west-southwest of Brawley, a city of roughly 26,000 residents located near the Salton Sea and about 15 miles north of the U.S.-Mexico border. Activity intensified with dozens of aftershocks, including magnitudes 4.5, 4.4 and 4.0, continuing into Sunday morning. Most quakes were minor, below magnitude 2.5, and occurred at shallow depths of five to 10 miles, making them more noticeable to residents. Shaking was felt across the Imperial Valley, from the Coachella Valley to Mexicali, Mexico, and as far as San Diego, with over 165 "did you feel it" reports submitted to the USGS.

The California Governor's Office of Emergency Services activated enhanced monitoring protocols, using USGS data from systems like the Prompt Assessment of Global Earthquakes for Response and...