The quake, centered 6 miles east-northeast of Milpitas along the Calaveres Fault, was relatively shallow, occurring 6 miles underground. NBC Bay Area audience members and Twitter users reported shaking as far away as San Rafael and Walnut Creek, as well as in San Francisco, San Jose, Menlo Park and Dublin.
Twitter user xtinasf told NBC Bay Area, "Felt very much so over here -- house shook for like 40 seconds ... in Walnut Creek."
At the other end of the Bay Area, Twitter user jonjayh reported, "It rattled the windows really well in South San Jose."
At least 10 aftershocks hit following the initial jolt, ranging from 1.5, to 2.3, according to the USGS. VTA and BART workers inspected the tracks to make sure the routes are still secure -- a routine precaution following any earthquake.
There were no immediate reports of injuries or damage.
Getting ready for the next one: The Red Cross Bay Area's earthquake safety guide
A check of the USGS recent earthquakes list shows the Calavares Fault has been fairly active over the past few days. Thursday's quake comes just a day after another one that rattled the South Bay. The USGS says an earthquake measuring 2.8 magnitute hit about 5 miles north of Alum Rock just after 11 p.m. Wednesday. While it wasn't a very strong one, many people reported feeling the shaker.
The USGS maintains earthquakes can't be predicted but a group of scientists and technologists, who formed a group called Open Hazards, challenge that notion, saying scientific tools and sensor technology can be used as a way to forecast earthquakes.
From their Web site:
We provide a free, open, and independent assessment of hazard and risk due to major earthquakes, using a self-consistent, global, validated methodology.
Did you experience shaking? Take a picture and post your experience on So Bay.
View 4.1 Earthquake in Milpitas in a larger map