San Francisco

This city's decade-long real-estate boom is fizzling out, but it has left an important legacy: When the next big earthquake hits, San Francisco will be a much safer place than it was after the last major shake.

The lesson: Stringent government quake-safety regulations are crucial. But there is nothing like several waves of economic prosperity for these rules to translate into cities that are more likely to better withstand quakes of magnitude of the one in China last week.

Corbis (left); 365 Main Inc. San Francisco's 1989 quake caused damage in the Marina district, left. An office at 365 Main, right, meets the city's new codes.

Building codes in San Francisco and throughout California -- a state long on the leading edge of earthquake and disaster-preparedness -- have been beefed up significantly since the Loma Prieta quake in 1989 and the 1994 Northridge quake in Los Angeles. But the real-estate slump in the early 1990s meant relatively few private buildings were constructed to those new earthquake rules.

Then the property market bounced back, fueled by a wave of growth in high-tech and related industries. So many new office towers and condominiums have sprung up here since the late 1990s -- and so many old buildings have been renovated -- that many more people now work and live in buildings designed to survive major seismic events. Similar retrofits have taken place in older buildings in other parts of California such as Los Angeles and Berkeley, but San Francisco has been particularly aggressive.

"Obviously, the newer the buildings, the better they're going to perform in an earthquake," says Isam Hasenin, director of San Francisco's building-inspection department.

According to the U.S. Geological Survey, the Bay Area has a 63% chance of being rocked by a 6.7-magnitude or higher quake in the next 30 years. San Francisco's famous 1906 quake was around the same size as the 7.9 quake in China last week. Loma Prieta, 83 years later, measured 6.9.

After the 1989 temblor, San Francisco began retrofitting public buildings like the historic City Hall. The state started shoring up highways and bridges, such as a $6.3 billion overhaul of the San Francisco-Oakland Bay Bridge that is still under way. And the state and city passed more-stringent building codes for public and private buildings.

It took the dot-com boom for those codes to start making a noticeable impact on private buildings in some of the most critical areas of town. In the late 1990s, young entrepreneurs invaded the city's South of Market Street area, dubbed "SoMa," a gritty industrial neighborhood filled with unreinforced brick and concrete buildings that could topple in a quake. To convert these buildings into offices, landlords had to make major seismic enhancements.

One retrofitted building is 365 Main, a four-story structure that houses corporate-data centers for big companies. The building, a former concrete warehouse built around World War II, was first redeveloped by a tech start-up called AboveNet Inc. in 2000.

Engineers from Skidmore, Owings & Merrill LLP installed 98 sliding "isolation bearings" underneath it, which sit on top of the reinforced concrete columns supporting the building; the bearings will help absorb the shaking of a quake. Before the retrofit, the building had been abandoned and was seismically deficient, says Peter Lee, an associate director at Skidmore Owings.

San Francisco officials after the 1989 quake identified about 2,000 dangerous unreinforced masonry buildings in the city. To date, about 95% of these buildings have been retrofitted.

To be sure, there is no guarantee that even the best-designed buildings will withstand a killer quake. There are also fewer seismic regulations governing existing buildings than new ones.

"There are weak buildings out there," says Thomas Brocher, a seismologist with the U.S. Geological Survey in Menlo Park, Calif. But compared with the period before 1989, "in some ways, we are more prepared" for a big quake today, he says.

Write to Rebecca Buckman at rebecca.buckman@wsj.com

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