[jlousa]

Did you read the very reports commissioned by the city and linked to in this thread several times? The viaducts are not at risk of collapse during an expected earthquake. It would take a 1/1000yr quake to damage the viaducts to the point they would most likely not be usable. The viaducts were already seismically upgraded once and the report gave recommendations on what would be needed to survive the "big" one.