It’s been two decades since a 6.9- magnitude earthquake jolted San Francisco, killing 63 people, yet thousands of apartment buildings prone to collapse have never been shored up to withstand another large shock.
There are more than 17,000 so-called soft-story structures in the San Francisco region, including Silicon Valley, according to the Association of Bay Area Governments. Such residential buildings typically have large, open areas for parking or business on the first floor, leaving that story structurally weak. Los Angeles probably has a greater number, officials said.
The 8.9-magnitude earthquake that struck Japan on March 11 has safety experts concerned that California hasn’t done enough to bolster vulnerable buildings. The roadblock is a politically charged question: whether government should force property owners to pay for costly retrofitting. The debate is now complicated by the state’s $25.4 billion budget deficit, which is causing cuts in everything from schools to health care.
“That’s a difficult decision to make because a lot of people can’t afford to do it,” said Richard McCarthy, executive director of the California Seismic Safety Commission in Sacramento. “Retrofitting is expensive, particularly right now with all the foreclosures, so if you force somebody to retrofit, they aren’t going to be able do it.”
San Francisco’s mayor in 2009, Gavin Newsom, now lieutenant governor, directed the city’s Building Inspection Department to design a law requiring property owners to do the work. The Applied Technology Council, in a report commissioned by the city, estimated the cost to fix all of San Franciso’s soft-story buildings at about $260 million, or as much as $28,000 per residential unit.
San Andreas Fault
Applied Technology, a nonprofit corporation based in Redwood City, California, that studies engineering for natural disasters, said such a cost would offset the $1.5 billion in damage likely after a magnitude 7.2 earthquake on the San Andreas fault, which slices through the Bay Area.
The 6.9-magnitude Loma Prieta quake struck Oct. 17, 1989, just before the third game of baseball’s World Series at Candlestick Park in San Francisco between the San Francisco Giants and Oakland Athletics.
The temblor damaged about $6 billion in property and about $1.8 billion in the area’s transportation system, according to the U.S. Geological Survey’s Earthquake Hazards website.
Heavy damage in the city’s Marina district, crowded with apartments, was caused by liquefaction, a process where soil loses its strength after violent shaking.
A 1906 earthquake in San Francisco killed an estimated 3,000 to 5,000 people and set off three days of fires that razed most of the city. It was the greatest natural disaster in U.S. history until Hurricane Katrina struck New Orleans.
A 2008 study by the Geological Survey predicted that California would almost certainly be hit within 30 years by an earthquake as strong as the 6.7-magnitude temblor that struck the Northridge area of Los Angeles in 1994, killing 60 people, leaving 20,000 homeless and damaging 40,000 buildings.
Northridge and Loma Prieta were the two most costly earthquakes in U.S. history by insured losses, according to the Insurance Information Network of California.
“San Francisco and California have been very good on focusing on the days and weeks following a disaster, such as emergency preparedness,” said Sarah Karlinsky, deputy director of the San Francisco Planning and Urban Research Association. “But we’ve done a less-good job on what we need to be doing now to prepare our buildings.”
A 7.2-magnitude earthquake on the San Andreas fault directly offshore from San Francisco would make 27,000 buildings unsafe to occupy, according to a report late last year by the San Francisco Building Department. Fires ignited by the jolt would probably damage another 2,700 buildings.
The report, which projected about $30 billion in building damage, recommended that the city adopt an ordinance to require retrofitting by owners of any building deemed unfit to withstand an earthquake.
Since 1900, earthquakes have occurred in 39 states and have caused damage in all 50. A series of minor jolts rocked the state of Arkansas earlier this month. The last major temblor on the U.S. mainland was the 6.7-magnitude Northridge earthquake that struck Los Angeles in 1994.
In the wake of the Loma Prieta quake, California voters approved bond measures totaling at least $2.3 billion to retrofit government buildings, highways and bridges. In 1994, lawmakers ordered more than 2,700 hospital buildings to be shored up against earthquakes by 2013, at a cost the California Hospital Association pegged at $24 billion.
Peter Yanev, a structural engineer and the author of “Peace of Mind in Earthquake Country,” said California is running out of time to fix soft-story buildings, and probably needs to offer tax incentives to property owners to ease costs.
“It’s probably the most widespread class of buildings in the state that haven’t been strengthened in any significant way,” he said in a telephone interview. “It will probably only happen after the next big earthquake in California and a number of these buildings collapse.”
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