Magnitude 3.9 earthquake jolts the East Bay By KTVU staff 4.0 earthquake rattles the East Bay, widespread shaking felt A magnitude 4.0 earthquake rattled the East Bay on Monday. There were widespread reports of shaking but no reports of damage. KTVU Chief Meteorologist Bill Martin says the quake, with an epicenter near Castro Valley, was likely along the Hayward fault line. SAN LORENZO, Calif. - A magnitude 3.9 earthquake rattled the Bay Area Monday evening. According to the United States Geological Survey, the temblor struck near San Lorenzo around 6:29 p.m. The earthquake was first reported as a magnitude 4.2 but downgraded to a 3.9. There were no reports of danger or injuries. The shaker was felt in Oakland, Danville, Walnut Creek, and San Francisco.