BERKELEY, Calif. _ An earthquake centered in the Berkeley-Oakland area shook the Bay Area at 2:39 a.m. Thursday, according to the U.S. Geological Survey.
The 4.4 temblor, near the Claremont Hotel in the East Bay Hills, was along the Hayward Fault about eight miles deep, the USGS said. It's an area notorious for seismic risk _ and yet another reminder of the threat lurking from a fault that's the Bay Area's most overdue for a major quake.
The quake was originally reported as 4.7, but was later downgraded to 4.4 by the U.S. Geological Survey. It was widely felt from Santa Rosa to Gilroy.
"One would expect a lot of people to feel this size quake in the Bay Area," said USGS geophysicist Jack Boatwright, who awoke to a few seconds of shaking at his San Francisco home. "The motions look about half as strong as you would expect for this size earthquake."
Boatwright said the strongest ground motions were felt in the Emeryville area.
"Because of the size of the earthquake, we're on alert if it will possibly be a foreshock of a bigger quake," Boatwright said. "But there have been no aftershocks yet."
There were no immediate reports of damage, according to the California Department of Emergency Services.
Bay Area residents took to Twitter to share experiences. "WOW that was a good one folks, a solid jolt for 3 seconds here in San Francisco," wrote Drew Tuma.
For Northern Californians, the Hayward Fault is the most likely source of a dangerous quake, with a 31 percent chance in the next 30 years.
The Hayward Fault, part of the larger San Andreas Fault system, runs from San Pablo Bay in the north to Fremont in the south _ passing through the heart of Berkeley, Oakland, Hayward, Fremont and other East Bay cities.
The largest earthquake on the fault, estimated to have a magnitude of 6.8, occurred in 1868, according to the USGS. It killed about 30 people and caused major property damage.
But the population of the East Bay is now about 100 times larger _ so many more people will be affected by the next major quake.
The region is a place of ongoing and often imperceptible earthen creeping, as evidenced by routinely broken sidewalks in Hayward and Fremont. If you stand in the Bay Area and look toward the Sierra, over time you'd see the mountains move to the right.
The Hayward Fault creeps about one-fifth of an inch a year.
