A quake with a preliminary magnitude of 3.8 struck in Berkeley at 8:16 p.m. PDT, the U.S. Geological Survey said.
Thursday night's quake came nearly six hours after a magnitude 4.0 earthquake hit in the same area.
Berkeley police said there were no reports of damage or injuries from either quake.
Officials at Bay Area Rapid Transit said the system's trains Thursday night were experiencing minor delays as workers inspected tracks, a routine procedure after an earthquake.
Officials at Caltrain said none of its trains was delayed.
The second temblor was strong enough to knock photographs off the wall and glasses onto the floor at the home of Diane Coppini, who lives in nearby Emeryville.
"It was a nice jolt," Coppini said in describing the quake.
Seismologists determined that the second quake was an aftershock to the earlier quake, said USGS geophysicist Walter Mooney.
"This is a textbook example of an aftershock," said Mooney.
The earlier earthquake struck at 2:31 p.m. and was centered across the bay from San Francisco, six miles beneath the University of California, Berkeley, campus, according to U.S. Geological Survey maps.
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