SAN FRANCISCO (KRON) -- A 4.2-magnitude earthquake shook the Bay Area Monday morning at 7:01 a.m., according to the U.S. Geological Survey. The quake was the largest in a swarm that began with a 3.9-magnitude earthquake at 6:27 a.m. The epicenters are 2.6 miles southeast of San Ramon. Thousands of people reported feeling light to moderate shaking across the East Bay and San Francisco Peninsula, plus portions of the North Bay and South Bay, according to USGS’s “Did You Feel It?” survey. Nearly two dozen earthquakes at 2.5M or above were felt Monday morning: 6:27 a.m. - 3.8M 6:29 a.m. - 3.3M 6:48 a.m. - 2.5M 6:56 a.m. - 2.5M 7:01 a.m. - 4.2M 7:03 a.m. - 2.7M 7:06 a.m. - 2.5M 7:06 a.m. - 3.1M 7:07 a.m. - 2.8M 7:22 a.m. - 2.5M 7:23 a.m. - 3.0M 7:27 a.m. - 3.8M 7:32 a.m. - 2.6M 7:34 a.m. - 2.6M 7:36 a.m. - 2.8M 7:41 a.m. - 2.5M 7:42 a.m. - 2.8M 7:48 a.m. - 2.6M 7:54 a.m. - 2.8M 8:44 a.m. - 2.5M 9:03 a.m. - 2.5M (USGS) BART trains ran at reduced speeds following the 4.2M quake while track inspections were completed, transit officials announced. Commuters should expect residual delays on the BART system as normal service resumes. The National Oceanic and Atmospheric Administration (NOAA) said there is no tsunami threat from the 4.2M quake. There were no initial reports of damage or injuries. Monday's activity is the latest in a swarm of minor earthquakes centered on the San Ramon Valley over the past several months. "For this particular series of events, there is a very complicated set of faults," Robert de Groot with USGS told KRON4. "It’s just sort of crisscrossing each other in between Mount Diablo and the Calaveras Fault. When they start moving around a little bit, earthquakes happen; One thing moves another, another earthquake happens." ...read more read less