Update: Aftershock Felt After Earlier Quake

A 3.8 magnitude aftershock with a depth of 6 miles struck at 8:16 p.m., according to the US Geolocical Survey. It was very close to the earlier quake's location – two miles east of Berkeley.

BART officials said riders can expect 15-minute delays system-wide tonight.

------

3:00 p.m.

A 4.0 magnitude earthquake shook the Bay Area today at approximately 2:41 p.m., according to the US Geological Survey.

The earthquake's epicenter was two miles east-southeast of Berkeley and three miles northeast of Emmeryville.

All BART trains have been halted or slowed due to the  4.0-magnitude earthquake, a BART employee said. Trains systemwide are stopped or are traveling slowly as train operators conduct track inspections, the employee said. BART does not currently have an estimate for when the trains will resume normal operations.

The earthquake occurred on the same day as the Great California ShakeOut, a statewide drill in which millions of Californians practiced ducking and covering at 10:20 a.m. today.

The irony of an earthquake hitting on the same day as the statewide drill was not lost on Keith Knudsen, deputy director of the USGS Earthquake Science Center in Menlo Park, although he 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, he said. 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.

Did you feel it?

Bay City News contributed to this report.