Emerging data on last month's Northern California earthquake is explaining why the city of Napa suffered so much of the damage.

The 6.0 magnitude quake hit Aug. 24 from an epicenter about 5 miles south of Napa. Tom Brocher, director of the U.S. Geological Service's Earthquake Science Center, said Thursday that scientists have determined that most of the energy pushed north, up to Napa and the Napa Valley.

Broker says the fact that Napa Valley lies on sedimentary deposit rather than bedrock also meant that the shaking was longer and harder.

Brocher spoke after a session by seismic experts Thursday to share information on the quake, which injured more than 100 people. Speaking by phone, he said the earthquake shifted one side of the West Napa Fault northwards 18 inches.