EVEN NEW BUILDINGS AT RISK IN BIG ONE STUDY EXPLORES VALLEY IMPACT.
When the Big One hits, even the most advanced steel high-rises across the San Fernando Valley will be at risk of collapse, according to a recently published Caltech study.
A magnitude-7.9 earthquake could topple buildings built to standards in the latest codes, according to advanced 3-D supercomputer earthquake simulations.
While newer skyscrapers in the Los Angeles region could be damaged during a mega-quake, office towers in the Valley are vulnerable to ``probable collapse,'' report authors wrote.
``The potential for a large earthquake with a large amount of slip on the San Andreas Fault exists,'' according to authors of the report published this month by geophysicists at the California Institute of Technology. ``Our study indicates that serious damage could occur'' in older and newer steel-frame buildings.
Researchers used a cluster of 2,000 personal computers to simulate how 18-story high-rises would fare during magnitude-7.9 earthquakes along the San Andreas Fault. One from north to south would be far more damaging, the study concluded.
In that scenario, shock waves barrel 180 miles from Parkfield in the Central Valley and shake a hypothetical high-rise built to 1982 code standards on Canoga Avenue in Woodland Hills or in any of 636 other locations from eastern Ventura County to Orange County. The buildings collapse. So do the same hypothetical buildings constructed to 1997 standards.
``I don't worry about it till I feel the shaking. Then I think about it for a month. Then I forget about it,'' said James Kinsey, who works in a 12- story Warner Center high-rise.
The last magnitude-7.9 earthquake to affect the region was in 1857. Seismologists say such a temblor occurs once every 200 to 300 years.
In comparison, the 1994 Northridge Earthquake was a magnitude-6.7 temblor that killed 57 people and cost $40 billion.
``It could happen any day; we just don't know when,'' said Karen Felzer, a seismologist for the U.S. Geological Survey in Pasadena. ``Having well-engineered buildings is the most important thing to ensure safety, so looking at how buildings stand up is very important.''
Some structural engineers said the new study reinforced other, less sophisticated computer simulations that cast doubt on the safety of midlevel high-rises, especially older buildings.
Others doubted a mega-quake would affect all office buildings the same way.
If anything, most agreed that advanced computer simulations can only make buildings safer.
The study was published this month in the Bulletin of the Seismological Society of America and is available at www.ce.caltech.edu/krishnan. The lead authors, Swaminathan Krishnan and Jeroen Tromp, both Caltech geophysicists, were traveling and could not be reached for comment.
``The conclusion is that the effects could be somewhat higher than anticipated, the damage levels could be higher, with some ... collapse of taller buildings, even if they were built to code,'' said John Hall, a Caltech professor of civil engineering who did not participate in the study.
But Gary Hart, a structural engineer and division director at Weidlinger Associates, which analyzed the collapse of the World Trade Centers, disagreed.
He said such a study may have been subjected to more rigorous review if published in a structural-engineering journal.
``I think it's just dangerous to generalize,'' said Hart, a professor emeritus in civil engineering at UCLA. ``Each (building) is different. Some are L-shaped, some are square-shaped, some of them -- it depends on who the engineer is who designed it.
``In this business, you know who cuts corners and who doesn't.''
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|Publication:||Daily News (Los Angeles, CA)|
|Date:||Aug 15, 2006|
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