The last of a series of building code revisions based on the 1994 Northridge earthquake is expected to pass this month, making Los Angeles, already considered among the world's most quake-prepared cities, even more so.
But is it enough? Experts pondering the Northridge earthquake disagree over how well its lessons have been taken to heart.
Historically, changes made to the building codes of the city of Los Angeles after quakes "have saved so many lives, it's really a great success story," said Thomas Heaton, a Caltech professor of engineering seismology. "But at the same time, the range of things Mother Nature can throw at you is pretty big. . . . We don't really know what to fix."
Perhaps the most studied earthquake in history, the Northridge temblor produced reams of data and stacks of reports, but it has yielded fairly modest changes to codes so far--especially as they apply to existing buildings.
Of the dozens of changes the city has instituted since the quake, only a few have had or will have dramatic, immediate effects.
They range from aggressive measures requiring owners of hundreds of buildings to do repairs or retrofits, to deceptively minor amendments, such as one requiring designers and builders on the same projects to actually talk to each other.
The strictest new ordinances target two types of buildings: concrete tilt-ups, a common warehouse design, and steel-frame office buildings.
Owners of about 2,000 concrete tilt-ups built before 1976 must complete mandatory retrofits because of a rule passed immediately after the Northridge quake.
The buildings are mostly commercial and industrial structures, made by pouring concrete to form walls on the ground that are then tilted up and tied together. The buildings are considered hazardous because the walls tend to pull out, causing roof collapses during quakes, building officials said.
So far, about 1,300 tilt-up buildings are in some stage of retrofitting or demolition, said Tim McCormick, structural engineer for the city's Building and Safety Department.
The city then turned its attention to a more complicated problem: steel-frame buildings, which had been thought to be among the least vulnerable.
But the Northridge quake showed that they were flawed: A lower-cost type of weld that had come into vogue in the 1980s had tended to crack, meaning the buildings' skeletons weren't working as they were supposed to, moving flexibly to absorb energy.
Experts were caught by surprise. "The entire engineering community was freaking out," said Martha Cox-Nitikman of the Building Owners and Managers Assn.
The city passed a controversial measure requiring that owners of 243 such buildings within a specified quake zone inspect their structures and fix cracked joints if they found them.
The ordinance has had an effect, but progress is slow. With deadlines for repairs past, 217 buildings have been inspected or are in some stage of repair. Confirming fears, about 60% were found to have cracked joints, McCormick said.
The problem highlights some of the most difficult dilemmas involving retroactive codes.
Before the Northridge earthquake, the city had only once required owners to retrofit buildings, in 1981 when changes were ordered in unreinforced masonry structures.
That debate pitted City Councilman Hal Bernson against hundreds of landlords who didn't want to do retrofits.
Bernson won. When the Northridge earthquake hit, most of the 8,000 retrofits were complete. Without the repairs, experts said, the Northridge death toll would have been higher.
But in other areas, the payoff is not so clear.
Seismic safety codes are a nearly impossible mismatch between economic necessity and the murky world of earthquake science.
In the case of steel-frame buildings, there was disagreement about both the seriousness of the threat and the best way to fix the welds. To compound the problem, the program is very expensive, costing owners about $5,000 per joint to inspect welds, and $10,000 to fix them.
It was a politically sticky situation for the city. Today, some building owners believe they were punished for having deep pockets, while more dangerous buildings were given lower priority.
"When you talk about loss of life, there are so many other buildings that need to be dealt with," said Cox-Nitikman. "Why isn't the state doing something to help building owners, going from the most risky buildings to the least risky?"
Critics such as construction attorney Joel Castro, who represented families of those who died in an apartment collapse, call the city's response "laughable." Pointing out that no inspections were required in tall buildings downtown or in residential steel-frame buildings, he asserts that severe hazards remain.
"I don't know what it is about people, what it is about society," Castro said. "Everyone says, 'Well, it's political.' Well, it's life!"