The magnitude-4.8 quake struck at 4:55 a.m. at a depth of about 3.5 miles, said seismologist Amy Vaughn of the U.S. Geological Survey. It was centered two miles south of the small town of Bombay Beach on the eastern shore of the Salton Sea, about 90 miles east of San Diego.
The main quake was followed by at least 18 smaller aftershocks.
Salton Sea Beach resident Roberta Henderson told the The Desert Sun of Palm Springs that she was awake in bed when the quake hit.
"Lots of noise, some shaking, could hear all the wind chimes in the neighborhood ringing, then slow rolling, seemed to last longer than the actual quake," she said.
It was the largest in a swarm of earthquakes that have rattled the Salton Sea area since the weekend. More than 40 small quakes have been detected, most under magnitude-3.
Scientists are keeping close watch on the increased earthquake activity because it is near a section of the San Andreas Fault that has not popped loose in over 300 years.
The latest quake appears to have occurred in what's known as the Brawley seismic zone -- a "whole mess of faults" stretching between the Imperial and San Andreas faults, said seismologist Kate Hutton of the California Institute of Technology.
"It's really close to the San Andreas," she said.
A rupture on the southern San Andreas could set off the "Big One" that would devastate a large swath of Southern California. Scientists said there's a 5 percent chance that Tuesday's quake is a precursor to a larger event, but the probability decreases over time.
Last year, scientists estimated that a magnitude-7.8 earthquake on the southern San Andreas could cause 1,800 deaths and $200 billion in damages.
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