More activity is likely this week after a cluster of earthquakes that produced shaking from Orange County and San Diego east to Arizona occurred throughout Sunday at the south end of the Salton Sea.
"What we're seeing is a classic Brawley seismic swarm,'' said USGS seismologist Lucy Jones. "The area sees lots of events at once, with many close to the largest magnitude, rather than one main shock with several much smaller aftershocks."
Several quakes, the largest measuring magnitude-3.4, were reported early Monday. A magnitude-4.2 quake hit at 7:01 p.m., about two miles from Brawley, according to USGS.
Photos: Earthquake Emergency Kit
Seismologists said the quakes might continue for a few days, possibly a week or longer.
"It happens to be an area where instead of having a sequence that begins with a main shock then is followed by smaller aftershocks, this builds up and has several earthquakes that are sizeable then slowly dies off," said Dr. Kate Hutton, Caltech seismologist. "People down there should maybe not put the china back on the shelves yet."
The earthquakes shattered windows in downtown Brawley buildings and left 21 homes red-tagged. Patients were transported to another medical center after power was knocked out at Pioneers Memorial Hospital.
The largest of the quakes, magnitude-5.5, was reported at about 2 p.m. Another quake about an hour and a half earlier registered magnitude-5.3.
At least 300 aftershocks followed, and seismologists said shaking is likely to continue in the area for several days.
"It felt like there was quake every 15 minutes. One after another. My kids are small and they're scared and don't want to come back inside,'' Mike Patel, who manages Townhouse Inn & Suites, told the Associated Press.
A TV fell and some light fixtures broke inside the motel, Patel said.
The quake cluster occurred in a transition zone between the Imperial and San Andreas faults. Seismologists did not assign the earthquakes to either fault.