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Scientists believe the tectonic system beneath Los Angeles is fully capable of producing tremors up to a magnitude of 7.5, or about 15 times the energy of the 20-second Northridge quake. What would happen if that pulse roared for 40 or 50 seconds--higher-magnitude quakes typically shudder for 60 seconds or more--through the Elysian Park fault under downtown Los Angeles? ``The only way to get a full picture of how buildings react in an earthquake is to have one,'' says Thomas Heaton, a Geological Survey seismologist. But computer simulations undertaken by Heaton and collaborators show that steel- frame high-rises could have their feet kicked out from under them, and low buildings sitting on spongy pads could be smashed against their concrete foundation walls.
A year later, hidden damage is turning up in many steel-frame buildings that appeared to withstand the Northridge quake. Of 300 buildings inspected, reports Karl Deppe, an assistant chief with the Los Angeles department of building and planning, 100 sustained dangerous cracks, mostly in the welds at building joints, and the other 200 are ``suspicious.'' Many are office buildings in which people are still working, blissfully unaware of any damage. ``Repair has to be done,'' says Deppe. But the potential cost is enormous: anywhere from $750,000 to $2.4 million just to inspect the 500 to 600 joints in a single 20-story building, plus $15,000 to $22,000 to repair even one damaged joint.
Engineers and local politicians are arguing whether the joints should merely be restored to their prequake state or upgraded, whether such upgrading is even possible and, if it is, what is the best method. Similar debate swirls around how to revise building codes to do better in new construction and, even more important, how to retrofit older buildings--and who will pay the bill. Says Iwan of Caltech: ``The really difficult issue is what to do with the existing stock of less-safe, potentially hazardous structures. They're already built and paid for, there is probably a different owner, and now you've discovered there's a flaw. Who is responsible, the owner or the original builders?''
In Los Angeles there is only one rather minor incentive to retrofit: low-cost city loans to repair unreinforced masonry. San Francisco, says Iwan, more than five years after the Loma Prieta quake, is ``having a great deal of difficulty implementing anywhere near the kinds of retrofit regulations and laws that Southern California has,'' even though ``there are some very hazardous buildings there,'' many concentrated around Chinatown. In an era of government cutbacks, neither the state nor Washington seems likely to foot the bill. Insurance companies are not much help either. After picking up about half of the $20 billion losses from Northridge, most have stopped selling quake insurance.