Keay Davidson and Wyatt Buchanan
(www.sfgate.com)
Thursday, March 1, 2007
(03-01) 22:02 PST -- A 4.2 magnitude earthquake near Lafayette shook the Bay Area, just one week after a smaller quake in the same region.
There's no cause for alarm, however, and judging by preliminary evidence, the Thursday evening quake is just another reminder of continual slippage on Bay Area faults, a leading U.S. Geological Survey expert said.
"This is just a reminder that we all should ask ourselves, 'Do we have an earthquake kit in the car?' " USGS geophysicist Ross Stein told The Chronicle late Thursday.
It wasn't immediately clear which Bay Area fault was affected. It appeared to be close to the northern segment of the Hayward fault, but it might also lie somewhere between the Hayward and Calaveras faults, Stein said.
The quake struck at 8:40 p.m. and occurred at a depth of 10 miles. A USGS Web site indicated the epicenter was 1 mile northeast of Lafayette, 3 miles west-southwest of Walnut Creek, and 20 miles east-northeast of San Francisco City Hall.
There were some reports of damage, including a broken water pipe that caused the flooding of a business complex lobby on Taylor Boulevard in Pleasant Hill. In another case, a woman in Lafayette told authorities that her water heater detached and flooded her basement, according to a dispatcher with the Contra Costa Consolidated Fire District. BART officials said the shaking did not damage any tracks in the region.
At Postino Restaurant in Lafayette, host Nahal Afshar said the people gathered for dinner went silent when the shaking started.
"It lasted maybe five or six seconds. At first it was kind of jolty, then it shook side to side; it felt like it was vibrating beneath you," Afshar said. Nothing was damaged at the restaurant, she said.
Some diners and drinkers at the Pyramid Alehouse in Walnut Creek panicked as the ground shook and glasses above the bar clanged, said host Thomas Cantu. No one's drink fell over, though.
"It was definitely the strongest earthquake I've felt," Cantu said. "There were definitely a lot of screaming people. People didn't know what it was." At Stanley Middle School in Lafayette, the quake's jolt and rocking motion gave quite a scare to the 70 parents who had gathered in the music room to hear a concert by students. Michael Hang had just begun playing Debussy's Arabesque when everything started shaking, but he didn't miss a beat.
Last Friday, a 3.4 magnitude quake struck 7 miles deep on the Hayward Fault 2 miles east of Berkeley. Despite the coincidence of two noticeable quakes only a week apart, "I don't see evidence that this is part of a larger process" that should alarm the public, Stein stressed.
Thursday's quake first registered as a 4.4 magnitude shake but was revised to 4.2 within minutes. "A 4.4 is still relatively small," he noted. "This is an active fault. It produces large earthquakes every several hundred years or so, and it produces a larger number of smaller shocks. This (Thursday's shake) is the behavior we would expect it to produce.
"Of course, I could be dead wrong. But the odds are in my favor."
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