The mainshock was magnitude 6.0 , with a depth of 11.3 km . The United States Geological Survey ( USGS ) estimated that 15,000 people experienced severe shaking , 106,000 people felt very strong shaking , 176,000 felt strong shaking , and 738,000 felt moderate shaking . The earthquake lasted 10 to 20 seconds , depending on location . At least twelve aftershocks followed , including one of magnitude 3.9 . The earthquake was the largest earthquake in the Bay Area since the magnitude 6.9 1989 Loma Prieta earthquake . Governor Jerry Brown declared a state of emergency due to the severe damage and the possibility of aftershocks . President Obama declared a major disaster for Napa and Solano counties
1989 Loma Prieta earthquake
1989 Loma Prieta earthquake
2014 South Napa earthquake