The quake struck at 2:09 a.m. about 8.1 miles northeast of Trabuco Canyon and 14.9 miles south-southwest of Riverside.
People reported feeling the shaking across Los Angeles, Orange and Riverside counties.
Prepare SoCal: Disaster Preparedness in Los Angeles and Southern California
USGS reported several small aftershocks followed the 4.0-magnitude earthquake, including a 2.2 at 2:50 a.m. and two others with a magnitude of 1.1. All were northeast of Trabuco Canyon.
There were no reports of any injuries or damage.
Watch our live ABC7 Quake Cam here: http://abc7.com/2440166/
The earthquake comes just two days after a 7.9-magnitude quake off the coast of Alaska triggered tsunami watches all over the West Coast.
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