SAN FRANCISCO (CBS SF) -- A 4.4 magnitude earthquake centered along a seismically active five-mile stretch of Hayward fault near the University of California, Berkeley campus and historic Claremont Hotel jolted the Bay Area awake early Thursday, according to the U.S. Geological Survey.
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 major damage or injuries.
The USGS initially registered the temblor as a 4.7 magnitude quake, downgrading it quickly to a 4.5 magnitude and later to a 4.4.
USGS Geologist David Schwartz said the quake struck in an area where there has been a number of jolts 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 3-4," he told KPIX 5. "So it is a hot spot along the fault and this morning's earthquake was the largest of that group."
Schwartz said the real question in the hours after the quake was "is this a foreshock of something larger? That's the concern."
USGS Deputy Director Keith Knudsen told reporters at an early morning news conference that there was a slight chance that the quake was a warning of a much larger shaker.
"Looking historically at all the earthquakes that have happened in California, about five percent of the time earthquakes are followed by larger earthquakes," he said. "So there is a low probability but there is some probability."
Knudsen said it wouldn't be a big surprise if a major earthquake struck on the Hayward fault. "The last big earthquake occurred in 1868 so we are about at the 150-year anniversary," said Knudsen. "We know from geologic excavations on this fault that big quakes happen every 150 years."
Knudsen said the quake was eight miles deep into the earth, explaining why the temblor was so widely felt.
"It was relatively deep for an earthquake on the Hayward fault," he said. "Shallower earthquakes are felt over smaller areas, deeper earthquakes the earthquake energy radiates to a much broader area."
The quake's epicenter was on Claremont Ave., right across the street from the historic Claremont Hotel and also about a mile away from Cal's Memorial Stadium.
It knocked items off the 24-hour Safeway's shelves in San Leandro according to a witness.
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.
Among those awaken by the quake was Bay Area 1980's R&B star M.C. Hammer.
Long-time San Franciscan Nancy Foley emailed KPIX 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."
"I am totally shocked it was centered in Berkeley on the Hayward Fault and only a 4.5."
In Daly City, the quake startled Linda Solorzano.
"Here in Daly City all rattled shook and woke me bolted up putting shoes on to run out / away if did not stop," she posted on the KPIX Facebook page. "Can't sleep.. waiting for aftershock."
Gina Solis posted on the KPIX 5 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."
Donnie Dorschler was awake in Mill Valley when the quake hit and emailed: "It was a loud hit and then a slow rumbling."
Up in Sebastopol, Jenner Ninemires said the quake took his farm house for a gentle ride.
"I felt the earthquake up here in Sebastopol," he email to KPIX 5. "I live in an old 100-year-old farmhouse built on pier blocks and she swayed gently back and forth....wheeeee."
In the Santa Cruz Mountains, Kim Vestal posted: "Heart still pounding."
Joy Joyner was sure the quake's epicenter was near her Morgan Hill home.
"Big shake woke us up, loud rumble, rattled everything," she posted. "Thought for sure it was centered down here."
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