The 6.0-magnitude earthquake, which hit at about 3:20 a.m. Sunday, was the most damaging in the San Francisco Bay Area since 1989 said David Oppenheimer, a seismologist with the U.S. Geological Survey in Menlo Park, Calif. The USGS predicted a more than 40% chance of aftershocks of a magnitude of 5.0 or greater during the next week.
“This illustrates what happens when a moderate earthquake hits where people live,” he said. “It can be quite serious.”
No deaths were reported as a result of the quake. In Napa, ambulances transported those hurt to a local hospital, where about 120 patients were treated, city officials said Sunday afternoon. Three major injuries had been reported.
Mr. Oppenheimer estimated potential economic losses could exceed $100 million due to the broad distribution of the quake, the effects of which spanned for miles.
The affected area includes Napa County, a major hub for the California wine industry that generates thousands of jobs and a yearly $13 billion for the local economy.
Winemakers in the region said they were still assessing the damage. Meanwhile, city officials encouraged visitors to continue coming but to avoid cordoned-off areas.
California Governor Jerry Brown declared a state of emergency Sunday morning, citing severe damage in Napa and other surrounding counties and the potential of aftershocks.
He ordered all state agencies to use their personnel and equipment to aid the areas affected by the earthquake, which he said resulted in the closure of major highways and roads and power outages for more than 69,000 residents. As of Sunday evening, a little over 7,000 customers remained without power, according to a spokesman from Pacific Gas and Electric Co.
The earthquake caused major damage to several downtown buildings, including a historic court house. Some of the structures had not undergone a seismic retrofit, a city spokesman said.
Fires caused by the earthquake destroyed four mobile homes. City crews worked to repair dozens of broken water and gas mains. A shelter was set up at the local high school gym.
State officials deployed first responders to assist in search and rescue efforts, as well as in dealing with fires and other possible emergencies, said Kelly Huston, deputy director of California Governor’s Office of Emergency Services.
An aisle of a Dollar Plus and Party Supplies Store in American Canyon, Calif. after an earthquake on Sunday. Associated Press
Mr. Huston said that the hardest hit area was Napa County, but he added that it is too early to assess the extent of injuries and economic loss.
The early morning jolt sent residents like Patricia Trimble, 50, scrambling outside their homes.
Ms. Trimble, who owns an antique and gift shop in downtown Napa, was at the site of her business, The Roost Napa, shortly after the quake hit. She found shattered glass, paints splattered on the floor and dozens of overturned items. She was still there six hours later sweeping up glass and picking through debris inside the shop.
“It’s just devastating—it is like a tossed salad,” she said. “Our house is destroyed. Everything just fell down. In the store everything is broken, but we are safe.”
A powerful 6.0-magnitude earthquake shook Northern California early Sunday morning, causing power outages and fires around Napa wine country. Photo: AP
The earthquake appears to have occurred on the West Napa fault, an area where no quake that size has been measured since record keeping began in the early 1900s, said Mr. Oppenheimer, the USGS seismologist.
The earthquake struck about 6 miles southwest of Napa. It was the biggest quake to shake the Bay Area since the 6.9-magnitude Loma Prieta quake in 1989, said Mr. Oppenheimer.
The timing of the earthquake was fortuitous, he added, with most people indoors or asleep.
Historic buildings with unreinforced masonry in downtown Napa, Calif., were damaged by the early-morning earthquake. Ramin Rahimian for The Wall Street Journal
Throughout the city of Napa roads were sporadically closed, power was out, helicopters flew overhead. A water main break flooded one street, and power outages left streetlights dark. Brick buildings appeared particularly hard hit.
Residents of the city of Napa wandered through the downtown area surveying the damage Sunday.
Glass was shattered on the storefronts up-and-down historic First Street and workers were busy putting up plywood where their glass windows had shattered. The Goodman Library, a historic building, was roped off with police tape; portions of its facade had tumbled onto the street.
Cynthia Langlois-Yallop, 45, the manager of the Uptown Theatre Napa, said much of the interior of the renovated art deco building in downtown had been damaged. She felt the quake at her home; she was still awake, having arrived home shortly before the shaking began following a concert at the theater Saturday night.
“It seemed like it was going on forever,” she said. “You could just hear things breaking, and books flying off bookshelves.”
A worker surveys an aisle full of wine bottles tossed from shelves at Van’s Liquors in Napa, Calif., in the aftermath of Sunday’s earthquake along the West Napa fault. Getty Images
—Jim Carlton contributed to this article.