The quake, which occurred at 2:57 p.m., was centered about two miles southeast of Pacifica, according to the U.S. Geological Survey.
In the Menlo Park area, people reported feeling a short rattle. An office worker in San Mateo said she felt a jolt. "I couldn't tell if it was an airplane crash or an earthquake. It was a booming jolt.
There were no initial reports of damage or injury.