Magnitude-4.0 earthquake rocks Bay Area

Show Caption Hide Caption Magnitude 4.0 earthquake rocks San Francisco area The U.S. Geological Survey said a 4.0-magnitude earthquake rattled the San Francisco Bay Area before dawn Tuesday. No damage or injuries were immediately reported. This comes less than a year after a deadly 6.0-magnitude quake hit South Napa.

SAN FRANCISCO — A magnitude-4.0 earthquake rattled the San Francisco Bay Area before dawn Tuesday, though no damage or injuries were immediately reported.

The U.S. Geological Survey said the quake struck at 2:41 a.m. PT. It was centered 2 miles northeast of Fremont, an Alameda County city of more than 220,000 people 30 miles southeast of San Francisco. A magnitude-2.7 aftershock follwed 15 minutes after the quake, then several smaller aftershocks rolled through the area.

Commuter rail service was delayed for about 20 minutes in the morning rush while Bay Area Rapid Transit officials inspected tracks for possible damage.

"We felt it. Lots of calls coming in from nervous and scared residents, but no reports of damage at this time," the Fremont police department tweeted.

A Fremont fire dispatcher told USA TODAY the city received no calls regarding the quake.

The rolling sensation of the quake was strong enough to wake residents and set dogs barking in San Francisco, but it did not hit with the strong impact that rattled the region in August. That magnitude-6.0 South Napa quake, which hit on Aug. 24, centered less than 70 miles from Fremont. It killed one person, injured 200 and caused $400 million in property damage.

Fremont is at the southern end of the Hayward Fault, which saw its most serious earthquake in 1868. Although its magnitude isn't known, that quake killed 30 people and was known as "the great San Francisco earthquake" until the iconic, magnitude-7.9 quake along the San Andreas Fault in 1906.