Modern steel buildings have long been considered among the most sturdy in the event of a major earthquake. But a model of a massive quake in Southern California has sparked debate among scientists and engineers over whether these structures are more vulnerable than previously thought.
The Great Southern California ShakeOut, the nation's largest quake drill, suggested that about five high-rise steel buildings in the region would collapse in the modeled magnitude 7.8 quake.
High-rise steel buildings sustained less damage than unreinforced brick buildings and older concrete buildings in the analysis. But the damage they sustained was greater than expected based on the standard building design formulas.
"It has huge implications," said Lucile Jones, a U.S. Geological Survey seismologist who served as chief scientist for the ShakeOut project. "When these types of buildings collapse, we could have 1,000 people in them. That's something to worry about."
The findings come 14 years after the Northridge earthquake, which exposed weaknesses in some older steel buildings.
Jones said she hopes that policymakers will use the results of the November drill as they develop guidelines for retrofitting existing buildings and set standards for new buildings. But not everyone finds the ShakeOut scenario so worrisome.
Luke Zamperini, principal inspector for the Los Angeles Department of Building and Safety, said the scenario is interesting but doesn't necessarily demand action.
He was not convinced that an earthquake of that size would cause any steel high-rises to collapse.
"It's hypothetical," Zamperini said. Changing building codes "is based on forensics, on what we've seen happen. Engineers are not willing to make changes on what people theorize might happen."
Standard building design formulas rely on the average effects of earthquakes recorded worldwide, said Swaminathan Krishnan, an assistant professor of civil engineering and geophysics at Caltech who led the modeling. But information on earthquakes the size of the one modeled -- a magnitude 7.8 on the San Andreas fault -- is sparse, he said.
Simulations of this size became possible only in recent years, thanks to supercomputers that also allowed scientists to feed in specific geological and topographical details for Southern California.
The model produced a lot of long, rolling ground motions in the Los Angeles Basin that are problematic for tall steel buildings, especially those built before the 1994 Northridge earthquake.
