Tag: napa earthquake
Shaking From Napa Earthquake Was Highest Ever Recorded In Area

Shaking From Napa Earthquake Was Highest Ever Recorded In Area

By Rosanna Xia and Rong-Gong Lin Ii, Los Angeles Times

NAPA, California — The ground-shaking during the magnitude 6.0 Napa earthquake was the highest level recorded in modern times for downtown Napa, according to the U.S. Geological Survey.

The ground motion recorded in downtown Napa came very close to the maximum level of ground shaking engineers use in their calculations when designing new buildings in that area, said Erol Kalkan, a USGS research structural engineer.

Newer buildings withstood the shaking and performed as expected, surviving with cosmetic damage, Kalkan said.

Longtime Napa residents described the earthquake as something particularly more violent than what they felt during the 1989 Loma Prieta earthquake and the 2000 Napa Valley earthquake.

“This one was very, very different,” said retiree Sherry Vattuone, 70. “My bed went up and down … like the ‘Exorcist’-type thing, and then it slid, and then all of a sudden there, it was like something took the house and went like this” — shaking her hand — “just as hard as they could.”

It wasn’t only her pasta bowls and half of her San Francisco Giants bobbleheads that were smashed in the quake: her home now leans askew, with her basement leaning at a sickly angle from the upper floor.

City officials said her home could not be occupied because the house had shifted from the underpinning foundation, and she was forced to move into a trailer a neighbor loaned her, parked outside her home, where she lives with her three dogs: Daisy, Dusty, and Duncan.

About 150 buildings have been red-tagged, meaning they are too dangerous to be entered, and about 1,000 more that are yellow-tagged, meaning there may be limited access to the structure due to damage, Rick Tooker, director of Napa’s Community Development Department, said Tuesday.

While strong for Napa, the Aug. 24 earthquake did not produce ground shaking as intense as was felt during the 1994 Northridge earthquake. That temblor produced ground motions about 50 percent more intense than what was recorded in Napa, said USGS research geologist Dan Ponti.

High-quality recordings like the one in downtown Napa provide valuable data and have only been available in the last two decades as more and more recording instruments have been placed throughout California, said David Oppenheimer, a USGS seismologist and project chief of the earthquake monitoring project.

During the 1989 Loma Prieta earthquake, for example, USGS had about 70 recordings that weren’t of that high a quality. If a similar earthquake occurred in the Bay Area today, the USGS would have about 400 instruments recording ground motions at a much higher quality, Oppenheimer said. “That would give us a much greater and varied picture of the earthquake,” he said.

AFP Photo/Josh Edelson

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Scores Of Aftershocks From Napa Earthquake Felt, More On The Way

Scores Of Aftershocks From Napa Earthquake Felt, More On The Way

By Hector Becerra and Veronica Rocha, Los Angeles Times

LOS ANGELES — There have been scores of aftershocks from Sunday’s 6.0 earthquake in Napa County, and experts said the small quakes will continue for days.

In general, the likelihood of big aftershocks goes down with time, as does the chance of a larger quake.

Officials have warned the public to be careful around damaged buildings because even a small aftershock could knock debris loose.

At least 65 aftershocks have rattled Napa and its surrounding areas since the destructive 6.0-magnitude earthquake struck early Sunday, according to the U.S. Geological Survey.

Two of the 65 aftershocks were magnitude 3.0 or higher, said Susan Garcia of the USGS Earthquake Hazards Program in Menlo Park, Calif. The largest, a 3.6-magnitude aftershock, occurred around 5:47 a.m. Sunday, she said.

Sunday’s quake occurred on the West Napa fault. It’s about 20 miles, much shorter than the better-known Hayward and Rodgers Creek faults, which are capable of a 7.2-magnitude quake. Still, it produced the largest earthquake in the Bay Area since the deadly 6.9 Loma Prieta quake in 1989.

The shaking was dwarfed in magnitude and sheer destruction by much larger earthquakes, such as the 1989 quake, as well as the 1971 and 1994 temblors in the San Fernando Valley.

But considering that Sunday’s earthquake ran less than half the length of the fault, scientists said the temblor could have been worse.

“This is one of the smaller of the sets of faults in the East Bay, but it’s still obviously large enough to create a magnitude-6 quake, and it didn’t rupture the length of the whole fault,” said Jeane Hardebeck, a seismologist for the USGS, also in Menlo Park. “If it had, you could imagine a much larger earthquake.”

Like a lot of faults, she said, it runs parallel to the roughly 800-mile-long San Andreas fault. Sunday’s quake happened just south of Napa and ran north along the fault, which runs on the western side of the Napa Valley, Hardebeck said.

The last time Napa was shaken hard by a destructive earthquake was Sept. 3, 2000, when a 5.2-magnitude quake struck the area.

On Monday, power had been restored to nearly all of the approximately 70,000 customers in Napa County whose lights went out after the earthquake struck early Sunday, utility officials said Monday.

The approximately 150 customers who remained without power were expected to have their service restored later Monday morning, according to Pacific Gas & Electric officials.

AFP Photo/Josh Edelson

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