San Francisco Bay Area rattled by 4.5 earthquake


San Francisco Bay Area rattled by 4.5 earthquake

A magnitude 4.5 earthquake was felt widely in the San Francisco Bay Area on Monday evening at 10:33 p.m., with the epicenter in the Walnut Creek and Pleasant Hill areas.

Moderate shaking was felt in the Pleasant Hill, Walnut Creek and Concord areas of an intensity that can overturn unsecured objects, such as books and picture frames, and is capable of breaking dishes or windows. Weak shaking was felt in San Francisco, Oakland and San Jose, according to the U.S. Geological Survey.

Close to the epicenter in Walnut Creek, there was strong side-to-side shaking, strong enough to knock CDs off a shelf.

Based on the observed shaking intensity recorded by the USGS, scientists said they don’t expect there to be major structural damage.

The earthquake had a preliminary depth of about 9 miles underneath the surface, fairly deep for this part of the world, Keith Knudsen, USGS geologist and deputy director of the agency’s Earthquake Science Center, said in an interview. Such a deep quake made it felt widely over a broad area, but lessened the shaking intensity felt at the surface than if it were shallow, scientists said.

The earthquake was not directly on top of any of the main Bay Area earthquake faults. The epicenter was about three miles west of the Concord fault, and farther than that off the northern end of the northern Calaveras fault, Knudsen said.

The epicenter is just northwest of Mount Diablo, one of the Bay Area’s tallest peaks. The Mount Diablo area is also a seismically active zone, “a region of uplift, folding and thrusting,” said David Schwartz, USGS scientist emeritus.

There were a series of earthquakes in the magnitude 5 range on the southeast side of Mount Diablo in 1980 in the Greenville fault area. On Jan. 26, 1980, a magnitude 5.4 quake hit with an epicenter only 6 miles from downtown Livermore. Damage in 1980 was reported at Lawrence Livermore National Laboratory and a mobile home park.

“Because any quake can be a foreshock, there’s a slight increase in the chance of a bigger quake for the next few days,” seismologist Lucy Jones said on Twitter.

The Concord-Green Valley and Calaveras faults are among the Bay Area’s most significant. The Concord-Green Valley fault is capable of causing damage to infrastructure systems and impact the entire Bay Area; the Calaveras fault can produce a magnitude 7 quake.

Near the epicenter, it seemed the worst impact was residents shaken from sleep.

At Farrington’s Sports Bar in Pleasant Hill, about 20 patrons were playing pool and darts and watching TV when the earthquake started.

Bartender Casey Ashimine said no bottles broke but it was definitely apparent that they were experiencing an earthquake.

“A good little shaker,” Ashimine said. “A couple people looked around, but nobody freaked out.”

Assistant Chief Chris Bachman of the Contra Costa County Fire Protection District, which provides emergency services to communities close to the quake’s epicenter, said that as of about 11 p.m., there were no reports of injuries or property damage related to the earthquake.

The earthquake occurred just three days before the 30th anniversary of the magnitude 6.9 Loma Prieta earthquake, which killed 63 people in Northern California.

In the last 10 days, there have been two earthquakes of magnitude 3.0 or greater centered nearby.

An average of 25 earthquakes with magnitudes between 4.0 and 5.0 occur each year in California and Nevada, according to a recent three-year data sample.

The earthquake occurred at a depth of 9.1 miles. Did you feel this earthquake? Consider reporting what you felt to the USGS.

Find out what to do before, and during, an earthquake by reading our five-step earthquake preparedness guide.

Times staff writer Mark Z. Barabak contributed to this report.




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