A water-main break flooded several floors of Brea City Hall, and the shaking knocked down computers and ceiling tiles, Stokes said.
Friday's jolt was the strongest to strike the greater Los Angeles region since 2008. Southern California has been in a seismic lull since the deadly 1994 Northridge earthquake killed several dozen people and caused $25 billion in damage.
The latest quake hit a week after a magnitude-4.4 centered in the San Fernando Valley shook buildings and rattled nerves.
It appeared to break a one-mile segment of the Puente Hills thrust fault, which stretches from the San Gabriel Valley to downtown Los Angeles and caused the 1987 Whittier Narrows quake that killed eight people. The rupture lasted half a second, scientists said.
U.S. Geological Survey seismologist Lucy Jones said it's unclear whether Southern California is entering a more active seismic period. "We have been in a really quiet time. It can't stay that way," Jones said.
Peter Novahof went shopping with his family at a hardware store in Long Beach a day after the quake. Though nothing was knocked out of his place at his home, he figured it was a good time to think about securing his television and cupboards with glassware.
"We've had an earthquake drought for a while," he said. So people are decorating their houses without taking into consideration that "we're in earthquake zone."
AP writer Daisy Nguyen contributed to this report from Long Beach, Calif.
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