The bigger quake was originally reported as magnitude 5.4 and struck at 9:09 p.m. PT. The first temblor hit about an hour before that.
Caltech seismologists said the 5.1 quake was at a depth of around one mile and was followed by at least 30 aftershocks, two greater than magnitude 3.0.UPDATE: Aftershocks rattle Southern California after 5.1 earthquake
Eyewitness News viewers from across the Southland, including in Northridge, Altadena, Palmdale, Torrance and Riverside, reported feeling the temblor. It was also felt by residents in northern San Diego County.
There were no immediate reports of significant damage or major injuries. But some viewers did send in photos of toppled furniture, as well as broken glass and mirrors. Videos and pictures from many stores also showed a huge mess after items flew off shelves.
Metro said no damage to the rail system was found following a check of all lines, and the Los Angeles County Department of Public Works said there were no issues immediately reported with the county's bridges or dams.
The Brea Police Department reported a rockslide on Carbon Canyon Road following the shaking. The department tweeted a photo of a car that struck a rock and overturned. The occupants in the BMW only sustained minor injuries. As of 7 a.m. Saturday, the road remained closed.
Embassy Suites in Brea was voluntarily evacuated due to the earthquake. Hotel guests have since returned to their rooms.
The Los Angeles County Fire Department was investigating reports of possible gas leaks in the Rowland Heights area. A water-main break occurred in Fullerton near Rosecrans Avenue and Gilbert Street.
Seismologist Lucy Jones said Friday's largest quake was probably 10 times larger than the March 17 magnitude-4.4 quake near Encino in terms of energy released.
City News Service contributed to this report.