Last Updated Jan 4, 2018 11:52 AM EST
SAN FRANCISCO — A magnitude 4.4 earthquake centered on the CBS San Francisco reports the quake struck at 2:39 a.m. and was felt throughout the East Bay, North Bay and San Francisco. While many were jolted out of their beds, there was no preliminary reports of damage.near the UC-Berkeley campus jolted the Bay Area awake early Thursday, according to the U.S. Geological Survey.
The USGS initially registered it as a 4.7 magnitude quake, downgraded it quickly to a 4.5 and then at 3:28 a.m. downgraded it again to a 4.4.
USGS Geologist David Schwartz said the earthquake struck in an area that has seen dozens of smaller quakes over the last decade.
"It is centered on about a five-mile long section of the Hayward Fault that in the past 10 years has produced 30 earthquakes of magnitude between 3 and 4," he told CBS San Francisco. "So it's a hot spot along the fault, and today's earthquake -- this morning's earthquake -- was the largest of that group."
"The real question is: is this a foreshock to something larger? That's the concern," he said.
USGS Deputy Director Keith Knudsen told reporters at an early morning news conference there was a 5 percent chance the quake was a warning of a much larger shaker.
"Looking historically at all the earthquakes that have happened in California, about 5 percent of the time earthquakes are followed by larger earthquakes," he said. "So there is a low probability but there is some probability … It wouldn't be a big surprise if we had a big earthquake on the Hayward Fault. The last big earthquake occurred in 1868 so we are about at the 150-year anniversary …We know from geologic excavations on this fault that big quakes happen every 150 years."
Knudsen said the quake was 8 miles deep into the Earth, explaining why the temblor was so widely felt. The USGS website said people reported feeling the quake about 40 miles south in San Jose.
"It was relatively deep for an earthquake on the Hayward Fault," Knudsen said.
The quake knocked items off the 24-hour Safeway's shelves in San Leandro.
Transit agencies reported there were delays during the early morning commute while they checked for any damage.
"Anticipate minor delays at the start of light rail service as VTA conducts routine system checks as part of its standard safety precautions following an earthquake recorded earlier this morning," San Jose transit officials said.
Long-time San Franciscan Nancy Foley said in an email to CBS San Francisco that the quake felt much larger than the initial 4.5 estimate.
"HOLY COW! I'm in the Richmond District-SF, and it felt like a 5.5!!!," she wrote. "I'm also a native and lived through a large one in the late 50's as a kid, and the Loma Prieta in '89, while I was in an elevator…This one built to a cracking crescendo, similar to the last part of the '89. I thought my wall of bookcases would fall down."
Gina Solis posted on CBS San Francisco's Facebook page that it rocked her home in San Rafael.
"I felt it in San Rafael," she posted. "It shook our house and shook the bed big time!!!"
Pamela Jones posted: "Felt stronger than 4.5, in Concord."
In the South Bay, Chris Defayette said it was "a quick jolt."
"Yes in Campbell was a quick jolt and rocking," DeFayette posted.
Like hundreds of others, both Shannon Gonsalves in Alameda and Acacia Walls in Novato said the shaking was so strong it quickly awoke them from a sound sleep.
"Woke us up in Alameda," posted Gonsalves while Walls posted: "In Novato and jolted me awake while my bed was rocking."