The initial quake was relatively shallow, at a depth of 4.6 miles, the U.S. Geological Survey said. The epicenter was located about 1 mile south of La Habra, Calif., and 2 miles west of Brea, Calif.
Lucy Jones of the USGS said there a 5 percent chance the quake was a foreshock of a larger trembler.
"There could be even a larger earthquake in the next few hours or the next few days," Jones said during a media briefing.
A rock slide in Carbon Canyon caused one car to overturn, the Brea Police Department reported.
Several people experienced minor injuries due to the shaking.
Preliminary reports indicate the earthquake was centered along the Puente Hills thrust, which stretches all the way to downtown Los Angeles.
"This is the fault that could eat L.A.," seismologist Sue Hough told The Times in 2003.
[Los Angeles Times]