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When it comes to earthquakes, southern Napa County has more to worry about than the West Napa Fault.

The city of Napa lies between the Northern Hayward/Rodgers Creek Fault that runs through Sonoma County about 15 miles to the west and the Green Valley Fault that runs through Napa and Solano counties several miles to the southeast. Each fault has built up enough tension for a magnitude 7.1 earthquake, according to a new report.

“They’ve got you on both sides,” said Jim Lienkaemper of the U.S. Geological Survey, one of the report’s authors.

The result could be a powerful shaking for the city of Napa area if either fault slips, according to researchers from the U.S. Geological Survey and San Francisco State University who wrote the report. An earthquake of magnitude 7.1 would release more than 30 times the energy as the magnitude 6.0 South Napa earthquake on Aug. 24 that has caused an estimated $600 million in damages.

The Green Valley Fault runs from the hills between Napa and Solano counties southward and crosses under Interstate 80 near the entrance to Jameson Canyon/Highway 12. It continues south along the edge of Fairfield’s Cordelia Villages area, under Suisun Bay and under Concord.