USGS pinpoints new spot where 6.0 quake originated

NAPA, Calif. (KGO) -- The U.S. Geological Survey has pinpointed a new spot where they think Sunday's earthquake originated. They initially said the quake's epicenter was on Milton Road southwest of Napa, near American Canyon. After some recalculations, however, they now say it was a couple of miles further to the west and south, on Buchli Station Road.

Work being done now to repair damaged sections of Maxwell Bridge in Napa is at the top of the "to do list" for Caltrans.

"It's a major priority and we want to make sure that it's safe," said Vince Jacala with Caltrans.

What these crews found was a combination of cracks around support braces, sections of exposed rebar, and pieces of the cement support system reduced to piles of crumbled rocks. But Caltrans says this is all according to plan.

"So in an earthquake, the bridge is made to give a little bit," Jacala said. "And it actually, obviously, did give a little bit. So it worked the way it was supposed to work."

Inspectors find more damage after Napa quake

According to the USGS, the 6.0 quake's epicenter was at the Napa Marina. One boat fell to its side there, while other areas of damage were surface level, extending to Maxwell Bridge and beyond. A freshly patched crack on Milton Road, east of the Napa River, shows where the road split.

"Some of that rupture patch actually reached the ground surface," said USGS Deputy Director Keith Knudsen in a phone interview. "And that's why there's cracking at the ground surface. We call that surface rupture."

Scientist believe most of the activity and energy for the rupture started eight to 12 kilometers below the earth's surface, extending 10 kilometers north of the Napa River and west of Highway 29.

"We're putting out these instruments so we can monitor aftershocks and better understand shaking and how that area responds to shaking," Knudsen said.

But understanding damage is still important. Engineers would like to keep as much of the concrete as possible from falling.

A huge piece of concrete that broke off Maxwell Bridge fell less than 10 feet from where a homeless man was sleeping; showing us once again that as bad as things are after the quake, they could have been much worse.