Southland's Buildings Still Vulnerable to Earthquakes 20 Years Post Northridge

Twenty years after the Northridge earthquake, steel-frame buildings throughout the Southland remain vulnerable to seismic ground motions, according to a study released Wednesday by Caltech and U.S. Geological Survey engineers.

Scientists used computer models of buildings to simulate how the structures would perform in moderate, strong and very strong seismic ground motions. The study used nearly 65,000 simulated ground motions produced by the Southern California Earthquake Center and the USGS.

The simulations showed that during very strong ground motions, buildings with fracture-prone welds are substantially more likely to collapse than those with sound welds, and are much more likely to sustain irreparable damage, making them more likely to be a total loss in a major earthquake.

"We're not saying that every building constructed before 1994 is going to collapse in an earthquake," said Tom Heaton, director of Caltech's Earthquake Engineering Research Lab. "We're saying that buildings continue to be in use that pose a greater risk of physical injury and financial harm than is necessary."

The Northridge quake hit before dawn on Jan. 17, 1994, leaving 57 dead, thousands injured, and causing more than $20 billion in direct damage. The quake was centered in the north-central San Fernando Valley.

- City News Service