A minor, 3.9-magnitude earthquake struck in the San Francisco Bay Area on Monday ... U.S.G.S. scientists to update the shake-severity map. An aftershock is usually a smaller earthquake that ...

A 3.7-magnitude earthquake shook the San Francisco Bay Area in California, the U.S. Geological Survey reported. The 7-mile deep quake hit about a mile from Pleasant Hill south of Concord at 8:49 a ...