FEELING THE FORCE

Ground acceleration in the Sept. 3 magnitude 5.2 Napa Valley earthquake reached 40 percent of the force of gravity, according to new shake maps issued by the U.S. Geological Survey. The 1994 Northridge quake had a peak intensity of 182 percent of gravity. Yet the temblor caused more injuries than any in California since the magnitude 6.7 Northridge quake, with damage that could reach $15 million. Most of the reported damage was south of the epicenter and therefore most of the Napa Valley’s famous wineries were not badly damaged.