2014 South Napa earthquake 2014 South Napa earthquake The 2014 South Napa earthquake occurred in the North San Francisco Bay Area on August 24 at . At 6.0 on the moment magnitude scale and with a maximum Mercalli intensity of VIII ("Severe"), the event was the largest in the San Francisco Bay Area since the 1989 Loma Prieta earthquake. The epicenter of the earthquake was located to the south of Napa and to the northwest of American Canyon on the West Napa Fault. Total damage in the southern Napa Valley and Vallejo areas was in the range of $362 million to 1 billion, with
1989 Loma Prieta earthquake was built on was filled marshland, and half was somewhat more stable alluvium. Because of new highway structure design guidelines—the requirement of ductile construction elements—instituted following the 1971 San Fernando earthquake, a limited degree of earthquake reinforcement was retrofitted to the Cypress Viaduct in 1977. The added elements were longitudinal restraints at transverse expansion joints in the box girder spans, but no studies were made of possible failure modes specific to the Cypress Viaduct. When the earthquake hit, the shaking was amplified on the former marshland, and soil liquefaction occurred. During the earthquake, the freeway buckled and twisted before the