Shake intensity Weak Light Initial quake Larger aftershock Note: Map shows the area with a shake intensity of 3 or greater, which U.S.G.S. defines as “weak,” though the earthquake may be felt outside the areas shown. All times on the map are Pacific time. The New York Times A minor, 3.8-magnitude earthquake struck in the San Francisco Bay Area on Monday, followed by a larger 4.2 magnitude earthquake and another 3.8 magnitude quake, according to the United States Geological Survey.