Updated: Yes, That Was An Earthquake

A 4.0 magnitude earthquake shook the East Bay this afternoon.

The quake hit at 2:41 p.m. It was centered in Berkeley, according to the U.S. Geological Survey.

In addition to being felt in Alameda, the quake rocked Berkeley, Oakland, San Francisco, Union City, San Leandro, Lafayette and the San Ramon Valley, among other places.

Berkeley police said they have not received any reports of damage or injuries but have gotten some calls about car and building alarms that were activated by the quake.

Keith Knudsen, deputy director of the USGS Earthquake Science Center in Menlo Park, said today's temblor was a standard Hayward Fault Line quake.

He said the temblor was of the typical "strike-slip" variety, in which two sides of the fault slide horizontally.

Knudsen said the USGS had not yet recorded any aftershocks and that there is a roughly 5 percent chance that this afternoon's quake could be a foreshock to a larger seismic event.

Mother Nature certainly has good timing. Today many around the Bay joined an estimated 8 million Californians who participated in .

Students and faculty at the University of California at Berkeley also participated in the drill called ShakeOut, sounding a siren across campus this morning, school spokeswoman Janet Gilmore said.

There are no reports of serious damage or injury. However, BART has delayed trains up to 15 minutes systemwide to conduct safety checks.

If you'd like to share what you felt with the USGS, click here to fill out their Did You Feel It? form.

Updated: , five hours after this one, and having a preliminary magnitude of 3.9.