The quake struck at about 5:31 a.m. and had a depth of 6.3 miles, according to the U.S. Geological Survey. The temblor was centered 1 mile northwest of Pacifica, 4 miles west of San Bruno and 10 miles southwest of San Francisco, the USGS reported.
Bay Area Rapid Transit and Caltrain service have reportedly not been affected by the earthquake this morning.