The first of the quakes, magnitude 4.2, struck at 9:53 p.m. and was followed minutes later by magnitude-quakes of 3.9, 3.8 and 2.9, respectively.
Over the next hour, at least 11 more quakes struck, measuring 2.7 or less.
All were centered six to seven miles northeast of Simi Valley and were believed to be aftershocks of the deadly 1994 Northridge earthquake, said Lucy Jones of the U.S. Geological Survey in Pasadena.
There is no reason to believe they are a precursor to a bigger quake, Jones said.
"To feel another event, another three or so this evening, wouldn't be a surprise," Jones said. "But there's nothing about this that tells us, 'Oh, now we need to experience bigger in the next few days.' We had a very similar aftershock back in February."
The first and largest of the quakes was felt across much of Los Angeles' San Fernando Valley as well as throughout Ventura County to the north and even as far north as Santa Barbara, about 60 miles from the epicenter.
There were no immediate reports of damage or injury, said police Lt. Ken Tacke, who added that everyone at the Simi Valley police station felt the first of the temblors.
"It was fairly mild. It was a small, quick jolt and then right after that a much harder jolt," said Associated Press photographer Mark Terrill, who lives in Simi Valley.
Carlos Pena, a manager of a Denny's restaurant near the center of town, said no pots or pans fell during the shaking, but patrons became uneasy.
"The customers got a little panicky," Pena said. "Most of them stood up and tried to get to the cash register to pay quickly, and one girl couldn't wait and she started to make, kind of like, screaming noises."
Jones said all of the quakes were aftershocks of the Jan. 17, 1994, Northridge quake.
That magnitude-6.7 temblor, centered a mile south of Los Angeles' Northridge section, in the San Fernando Valley, caused more than 70 deaths and about $15.3 billion in insured losses. About 114,000 homes and buildings were damaged.
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