The U.S. Geological Survey is reporting a magniitude 4.1 earthquake whose epicenter appears to be about six miles east of Milipitas, Calif.
Twitter is abuzz with tweets from people who felt the tremor.
We'll update as soon as we know more.
Updated at 1:35 PM ET -- The USGS has received more than 4,800 responses from the public reporting on the intensity of the quake. Most people reported that the shaking was light and there was no damage.
Updated at 1:27 PM ET -- The San Jose Mercury News website reports the following:
The last magnitude 4 quake in the South Bay was March 30, 2009, when a 4.3 temblor struck just south of San Jose.
The last major earthquake in the Bay Area was the 1989 Loma Prieta earthquake -- a magnitude 6.9 quake that struck on Oct. 17, 1989, in the Santa Cruz Mountains. It killed 62 people and caused $6 billion in damages.