Bombay Beach, California - A moderate earthquake struck Tuesday on the edge of the Salton Sea in Southern California's Imperial County, but there were no immediate reports of any injuries or damages.

The magnitude-4.7 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 three miles south of the small town of Bombay Beach, or 90 miles east of San Diego.

A magnitude-3.0 quake shook the same spot about three minutes later, immediately followed by a magnitude-3.6 a few miles to the north.

An Imperial County sheriff's deputy who identified himself only as Sanchez said he felt shaking while he was driving his car in Salton City, 13 miles from the epicenter, but thought it was the wind. He said he had no reports of any damage.

Bombay Beach has been shaken by more than four dozen small earthquakes since the weekend, and scientists are keeping close watch on the area because it is near a section of the San Andreas Fault that has not popped loose in over 300 years.

Vaughn could not immediately say whether Tuesday's quake was on the San Andreas or one of several smaller faults in the area.

A rupture on the southern San Andreas could set off the "Big One" that would devastate a large swath of Southern California. Last year, scientists said a magnitude-7.8 earthquake on the southern San Andreas would cause 1,800 deaths and $200 billion in damages.