LOS ANGELES — The earth lurched without warning before dawn, jolting Los Angeles from its sleep. In a flash, freeway overpasses collapsed. Buildings were leveled or ruined. Fires spread.
Two decades after a magnitude-6.7 earthquake shattered Los Angeles and surrounding communities, buildings around the region remain vulnerable. While there has been progress to rebuild and shore up freeways and hospitals, there has been less attention paid to concrete buildings and housing with ground-floor parking.
“That remains a significant problem. We really have not come very far,” said Jonathan Stewart, an earthquake engineer at the University of California, Los Angeles.
At 4:31 a.m. Jan. 17, 1994, the ground shuddered beneath Northridge. After the shaking stopped, sections of the city laid in tatters. Several dozens died and 9,000 were injured. The quake caused $25 billion in damage. The largest cluster of deaths occurred at the Northridge Meadows complex, where 16 people were killed when their first-floor apartments crashed onto the parking garage below.
The city doesn’t keep count of how many so-called soft-story buildings exist and doesn’t require mandatory repairs even after 1994 because many such buildings survived the shaking. The Los Angeles Department of Building and Safety recently proposed surveying 30,000 apartments built before 1978 to determine which might be compromised during violent shaking as a first step toward possible retrofitting. The department has yet to receive funding to start the work.
After Northridge, the city required fixes to some 200 steel-frame high-rise buildings that unexpectedly suffered cracked welds and 2,750 concrete tilt-up buildings. Both types of repairs were relatively easy and did not bankrupt property owners. Even so, computer simulations released this week by the California Institute of Technology and U.S. Geological Survey found mid-rise steel buildings performed differently depending on the type of welding.
Other retrofits were voluntary, including efforts to buttress concrete-frame buildings. There are about 1,500 such buildings in Los Angeles County and between 16,000 and 17,000 statewide. Only about 10 to 15 percent are considered dangerous, said Craig Comartin, who led a study by the Concrete Coalition, a volunteer group of scientists, engineers and governments.