The strongest earthquake to hit California in 25 years shook buildings in the region north of San Francisco on Sunday. The quake, measuring 6.0 magnitude, damaged buildings in Napa, including the county courthouse and several other historic brick buildings downtown, reported the New York Times ("Losses From California Quake Could Top $1 Billion"). Though many had been retrofitted to withstand earthquakes in recent years, they did not hold, and large sections of brick and concrete collapsed onto the sidewalks. Many more buildings, including the county administrative building, had interior damage — broken sprinkler lines and fallen ceilings.
To view "quadcopter" footage of some of the building damage, watch the video below.
The earthquake Sunday was the strongest earthquake to rock the region since the magnitude 6.9 Loma Prieta quake in 1989. Both were relatively small compared to other California quakes in recorded history. The 1906 San Francisco earthquake, for example, was 500 times stronger than the quake that hit Sunday.
According to the U.S. Geological Survey, the economic losses could top $1 billion. Damage to buildings is expected to total much less. Still, more than 100 structures were affected, and much of the damage to older buildings confirmed the greatest fears of structural engineers – that retrofitting of older, unreinforced masonry building still leaves weak joints between bricks, reports the L.A. Times ("Even buildings with seismic retrofits damaged in Napa earthquake")
“We can’t keep every single brick in place in many of these older buildings without extraordinarily costly retrofits,” said Fred Turner, a structural engineer with the California Seismic Safety Commission. “We can reduce the damage in losses, but not eliminate them entirely in older buildings.”