The clusters of earthquakes have all been underneath the East Bay suburb of San Ramon, which is close to the Calaveras fault. There were at least 19 earthquakes of magnitude 2 or greater on Monday alone.

A minor, 3.6-magnitude earthquake struck in the San Francisco Bay Area on Monday, according to the United States Geological Survey. The temblor happened at 9:07 a.m. Pacific time about 2 miles southeast of San Ramon, Calif., data from the agency shows. U.S.G.S. data earlier reported that the magnitude was 3.7.