A second earthquake centered near Berkeley struck the Bay Area tonight, according to the U.S. Geological Survey.
The quake, with a magnitude of 3.8, struck at 8:16 p.m. and was centered about 1 mile east of Berkley with a depth of 6 miles, the USGS said.
An earlier 4.0-magnitude earthquake, centered about two miles east-southeast of Berkeley, rattled the region at 2:41 p.m. today.
The evening temblor created a large jolt in San Francisco, and was felt in parts of the Peninsula.
The 4.0-magnitude afternoon quake had a depth of 6.1 miles, according to the U.S. Geological Survey.
The earthquakes occurred on the same day as the Great California ShakeOut, a statewide drill in which Californians practiced ducking and covering.
Students and faculty at the University of California at Berkeley participated in the ShakeOut, school spokeswoman Janet Gilmore said.
The irony of an earthquake hitting on the same day as the statewide drill was not lost on Keith Knudsen, deputy director of the USGS Earthquake Science Center in Menlo Park.
He said the afternoon temblor was a standard Hayward Fault Line quake of the "strike-slip" variety, in which two sides of the fault slide horizontally.
San Francisco Mayor Ed Lee urged all Bay Area residents to visit www.72hours.org for emergency planning resources and tips.