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. Monday, 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 2 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.
Caltrain service was not affected, and operations were not altered at San Francisco International Airport. Several aftershocks occurred in the same area throughout the evening, including a 2.4-magnitude tremor at 4:55 p.m. and a 2.2-magnitude quake 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.
For more information about the earthquake including a map of the region, visit earthquake.usgs.gov.