An earthquake with a magnitude of 3.4 and several smaller aftershocks rattled parts of the Bay Area Monday afternoon and evening.
Initially, the U.S. Geological Survey reported the quake had a preliminary magnitude of 3.8, which it has since revised numerous times. As of 9:50 p.m., the estimate of the strongest seismic event's magnitude was 3.4.
The largest quake, which occurred at 2:57 p.m., was centered about two miles southwest of San Bruno and two miles southeast of Pacifica, according to the USGS. It was followed at 3 p.m. by a second, smaller earthquake with a magnitude of 1.5. That quake was centered about two miles southwest of San Bruno and three miles southeast of Pacifica.
BART stopped its trains briefly to inspect the tracks after the first earthquake. Trains were running at normal speeds again Monday afternoon, but 10-minute delays were reported system-wide. Caltrain service was not affected, and operations were not altered at San Francisco International Airport.
The first quake was felt in parts of the Bay Area, including San Francisco and Oakland. Thom Ball, library manager of the Pacifica Sharp Park Library, said he felt it. "There was a sharp jolt that was preceded by a rumbling noise. That was it," Ball said. "No books fell off the shelves. No lights went off. We all just felt it," he said. Everyone seemed calm afterward, Ball said.
Several aftershocks occurred in the same area throughout the evening, including a magnitude-2.4 tremor at 4:55 p.m. and a magnitude-2.2 event at 8:35 p.m, both of which were centered two miles southeast of Pacifica. The quakes occurred on the 105th anniversary of San Francisco's Great Quake of 1906.
Bay City News Service contributed to this report.