The U.S. Geological Survey this morning reported a 3.0-magnitude aftershock about four miles southwest of Napa, the fourth this morning in the same area where a 6.0-magnitude earthquake struck on Sunday.
The 3.0-magnitude aftershock was reported at 6:45 a.m. and followed a 2.8-magnitude quake at 6:12 a.m., according to the USGS.
A 3.9-magnitude aftershock struck about two miles northwest of American Canyon at 5:33 a.m. today and a 2.7-magnitude quake was reported at two minutes later west of American Canyon.
The aftershocks caused further roadway damage on State Route 29 Southbound at the George Butler Bridge and State Route 37 Westbound at the Mare Island Bridge, the California Highway Patrol reported.
All other bridges and major thoroughfares have been visually inspected by CHP. No damage was noted upon visual inspection. Detailed inspections will continue to be performed by Caltrans engineers.
The initial South Napa earthquake hit at 3:20 a.m. on Sunday, Aug. 24, waking Bay Area residents as far north as Ukiah and as far south as Salinas. The earthquake was located about four miles northwest of American Canyon, six miles south-southwest of Napa and about seven miles below the earth's surface, USGS officials said. It was the strongest earthquake in the Bay Area since the 6.9-magnitude 1989 Loma Prieta earthquake that killed 63 people and injured 3,757.
Most of the damage was concentrated in Napa, northwest of the epicenter, as the rupture sent most of the quake's energy in that direction. Inspections of damaged buildings in Napa were reported as about 75 percent complete Monday evening, with a total of 70 buildings now deemed uninhabitable, city officials said. City officials have been conducting inspections throughout the day, and red-tagged an additional 21 buildings since Monday morning, Napa Community Development Director Rick Tooker said at a news conference.
More than 200 buildings have been yellow-tagged, meaning that residents and owners can return to clean and collect possessions but are unable to stay there for the time being, Tooker said. The city has posted a map showing tagged structures.
City Manager Mike Parness said that "significant progress" was made Monday, including repairs to 30 water lines that had been reported leaking of a total of 90.
All power has been restored to PG&E customers in Napa except in red-tagged buildings, Parness said. About 70,000 lost power immediately after the quake and 17,000 were still without power Sunday afternoon.
Street closures are continuing in the areas surrounding buildings at risk of collapse, but officials are working on building barricades surrounding those buildings so that portions of the streets can reopen.
There have been no additional injuries reported beyond the previous total of 208 and officials are not anticipating any more earthquake-related injuries.
Schools in the Napa Valley Unified School District will remain closed on Tuesday.
The Solano County Board of Supervisors will consider a resolution on Tuesday that would declare the county under a state of emergency to help cover an estimated $750,000 in damage at county facilities in Vallejo.
Also, Caltrans will receive $2 million in emergency relief funds from the U.S. Department of Transportation's Federal Highway Administration to repair infrastructure damage from Sunday's earthquake, Rep. Mike Thompson said Monday. Caltrans has identified damage to bridges and roads with preliminary cost estimates of $10 million, according to Thompson, the state's Fifth District congressman.
The quake caused surface cracking on state Highway 121 north of the Sonoma-Napa county line at Cuttings Wharf, and significant stress to joints on bridges, including the Napa River Bridge on state Highway 29, Thompson said.
Local agencies also will benefit from the funds for infrastructure repair, Thompson said.