San Francisco's residential west and south sides would bear the brunt of destruction in a major earthquake because the city's older stock of wooden, single-family homes and apartment buildings are particularly vulnerable, according to a draft of a seismic vulnerability report that the city commissioned.
The city has shelved the report over questions about its professional quality, but Mary Lou Zoback, the U.S. Geological Survey's regional coordinator on earthquake hazards for Northern California, extolled the report as "the most comprehensive look at a realistic loss estimation for any urban area in the United States." Zoback was part of an advisory committee that oversaw the report's preparation.
"San Francisco's Earthquake Risk," the product of a yearlong study prepared for the city Department of Building Inspection by the Applied Technology Council of Redwood City, predicted that in a magnitude 7.2 earthquake along the San Andreas Fault:
-- 29,862 buildings citywide would be destroyed by the shaking and post- earthquake fire.
-- 20,857, or 70 percent, of those structures would be in the residential Richmond, Sunset, Twin Peaks, Ingleside and Excelsior neighborhoods.
-- Total economic losses would reach $13.7 billion citywide, with $4.6 billion, or 34 percent, sustained in the neighborhoods and low-rise commercial strips of the Richmond, Sunset, Twin Peaks, Ingleside and Excelsior.
"Until this report, we weren't even thinking about the residential areas of the Sunset and Richmond districts," said Patrick Buscovich, a structural engineer who served on a Building Inspection Department advisory panel set up to assess the seismic vulnerability of private buildings in San Francisco. "We'd never grasped there was going to be a lot of housing losses there."
The report has a curious history. It was sought by the Building Inspection Department as part of a planning effort begun in 2000 to reduce earthquake losses in San Francisco.
In March 2003, the city's Building Inspection Commission, which oversees the Building Inspection Department, held one hearing on the 60-page report, then ordered work on the document, then 95 percent complete, to cease.
Commission members questioned the $355,000 cost of the study and contended that it duplicated U.S. Geological Survey information already available to the city.
"I felt (it) spun off ... redundant information," said architect Bobbie Sue Hood, the commission vice president. In an era of budget constraints, "We don't want to waste the taxpayers' money."
William Wong, the Building Inspection Department's deputy director, said he had additional concerns about the caliber of the work and whether the city was getting its money's worth.
"Some research work was missing. On maps it was difficult to distinguish what they were talking about," Wong said, citing what he considered to be deficient graphic imagery that was difficult to read.
Wong also faulted the report for excluding government-owned property in the Presidio, Golden Gate Park and on Treasure Island as well as documentation submitted to the department for reimbursement for the work.
To make its predictions, the authors at the Applied Technology Council used computer software prepared by the Federal Emergency Management Agency for estimating earthquake loss and seismological, geotechnical, structural and population data specific to San Francisco drawn from local, state and federal government sources, according to the report.
It estimates deaths, building damage and economic losses neighborhood-by- neighborhood for earthquakes of varying severity along both the Hayward and San Andreas faults.
Unlike previous analyses that concentrated on downtown and South of Market, the report foretells a humanitarian crisis after a 7.2 magnitude earthquake along the San Andreas as tens of thousands of residents are made homeless by the destruction of nearly 30,000 houses and apartments -- or about 9 percent of the city's housing stock.
Depending on the time of day, the report predicts between 366 to 651 people would be gravely hurt or killed instantly with thousands more sustaining minor to serious injuries.
Of the estimated $13.7 billion worth of destruction, about half would befall residential structures, according to the report.
The housing stock is said to be particularly vulnerable because of the prevalence of "soft-story buildings," structures that contain stories that are substantially weaker and more flexible in a horizontal direction, usually due to garage or extensive window openings at street level.
"Such a condition is common in San Francisco, where many buildings (especially houses) have off-street parking on the ground floor, resulting in a ground floor soft story," the report said. "Corner stores and commercial buildings also tend to have this condition, due to the lack of interior partitions in the retail commercial space and the large window openings on the street."
In the Sunset, for example, where this style of construction is prevalent, 34 percent of the economic value of buildings would be wiped out by a magnitude 7.2 earthquake along the San Andreas, the report predicts.
The long-range housing and economic consequences would be felt most by those residents who can least afford it, said Buscovich, the engineer and advisory committee member.
For example, he said, the city's stock of 146,000 apartments covered by the city's rent-control law -- which applies to buildings constructed before 1979 -- are particularly vulnerable due to their age.
These homes "will come back as $600,000 to $700,000 condos," Buscovich said.
Similarly, he said, the city's single-room occupancy hotels, the lowest rung of the housing ladder, concentrated in the Tenderloin, won't be resurrected. "You know that no one is going to build SROs again."
According to Daniel Shapiro, a structural engineer and member of the California State Seismic Safety Commission who also served on the advisory committee that oversaw the preparation of the report, the document was supposed to form the basis for the Building Inspection Department to draft a community action plan for seismic safety.
Had the Building Inspection Commission not halted the project, Shapiro said, the last chapter of the seismic vulnerability report would have contained recommendations, such as retrofit programs to shore up "soft-story" structures and building code changes.
"Experience in California has shown that residential buildings can be successfully strengthened to resist earthquake damage," the report says. "Such seismic strengthening is very cost-effective given the alternative of losing a large fraction of the city's housing, with hundreds of thousands of people requiring emergency shelter for months to years."
As for averting post-earthquake fire damage, it adds, "Simple measures such as strapping gas water heaters and requiring automatic gas shut-off valves in high-density 'conflagration breeder' neighborhoods can be cost- effective."
The stakes have left members of the advisory group critical of city officials for not making more of the study.
"What the city has paid for to date ($355,344) should be distributed to as many people as possible. It makes no sense to sit on it," Buscovich said.
To the contrary, said Wong of the Building Inspection Department, copies of the report have been available upon request by calling (415) 558-6131 or e- mailing William.Wong@sfgov.org.
After inquiries from The Chronicle, the Building Inspection Commission scheduled a discussion of the report at its next meeting at 9 a.m. Monday in City Hall Room 400.
