Most of the Bay Area roads, bridges, water systems, dams and levees fared well in Sunday's 6.0 earthquake near Napa, but the damage in the picturesque Wine Country town was a jolting reminder of the vulnerability of public services for 7 million people.
A Big One -- such as a 7.0 earthquake on the Hayward Fault that runs beneath heavily populated Oakland and Berkeley -- would inflict more damage to key infrastructure, experts said.
"This was a reality check for us," said Abby Figueroa, a spokeswoman for the East Bay Municipal Utility District, the water supplier to 1.3 million people in the East Bay. "If they had hundreds of main breaks from a 6.0 quake, we know we would have thousands from a 7.0 on the Hayward Fault, which slices right under our service area."
It's not that public agencies have ignored the risk.
Bay Area water systems, road and toll bridge operators and other public agencies have spent billions of dollars on seismic retrofits since the 6.9 Loma Prieta earthquake struck on Oct. 17, 1989, when the shaking broke water mains, severely damaged and destroyed businesses, municipal buildings and homes from Santa Cruz to Oakland, collapsed the Cypress Structure freeway viaduct in Oakland and disabled the east span of the Bay Bridge for months. Sixty-three people died.
Since then, some $8.6 billion has been spent on seismic retrofits to the seven state-owned toll bridges in the Bay Area, including $6.5 billion for the new eastern span of the Bay Bridge. Those retrofits will reduce the length of time that any of the structures will be knocked out in a big quake, but not eliminate them, experts said. Caltrans crews visually inspected the bridges after Sunday's temblor and found no damage.
"What happened with a relatively moderate quake in Napa is small compared with what will happen with a much larger quake in the more densely populated parts of the Bay Area," said Randy Rentschler, a spokesman for the Metropolitan Transportation Commission.
Napa, Vallejo and American Canyon suffered the worst of the damage Sunday with some road closures, broken water mains and gas line ruptures leading to fires and power outages.
On Monday afternoon, some 600 Napa properties still were without water service as other Bay Area public water systems dispatched work crews to help with repairs.
PG&E was close to restoring electricity service Monday afternoon to 150 customers still without power. There were still 20 natural gas outages as of Monday afternoon, the utility reported.
A few downtown Napa streets were closed for repairs, including Second and Third streets from Seminary to Soscol and Main Street from Third to Clinton streets. Old Sonoma Road also was closed from Buhman Avenue to Congress Valley Road. One pedestrian bridge on Clinton Street in Napa was closed because ankle bolts at the bottom of the bridge were sheered off, said Napa City Manager Mike Parness.
Caltrans made temporary repairs Sunday to keep open a buckled portion of Highway 121 near Highway 29 in the North Bay and was preparing more permanent repairs that could result in traffic delays.
U.S. Transportation Secretary Anthony Foxx announced Monday that the federal government is providing $2 million to Caltrans to fix roads and bridges in the Napa Valley. Caltrans has placed the damage at $10 million in a preliminary estimate, Foxx said.
State water officials said they found no problems during post-quake inspections of Northern California reservoirs and canals, and levees in the Sacramento-San Joaquin River Delta that are crucial to protecting water quality for 23 million Californians.
However, the Napa temblor managed to cause problems in a fairly new building in Martinez, where broken pipes caused flooding in the room with computer servers at the Contra Costa County District Attorney's offices. Cleanup crews, however, acted quickly, and no workers were displaced at the six-year-old building at Ward and Las Juntas streets.
Staff writers Tom Lochner, Rick Hurd, and Gary Peterson contributed to this story. Contact Denis Cuff at 925-943-8267. Follow him at Twitter.com/deniscuff.