David Perlman, Chronicle Science Editor 
The next major earthquake on the Hayward Fault - inevitable anytime now, experts say - will be the Bay Area's own Hurricane Katrina, affecting more than 5 million people, causing losses to homes and businesses of at least $165 billion and total economic losses of more than $1.5 trillion, scientists warn.
And that's from ground shaking alone. If major fires break out - think 1906 in San Francisco - the total losses would be far higher, they said.
The staggering numbers come from new predictions of losses resulting from a magnitude 7 temblor on the fault, in which ground shaking could spread from the quake's epicenter directly on the fault to communities as far off as Santa Rosa and San Jose - or beyond.
Seismologists and quake loss experts joined Thursday to report the latest assessment of what scientists call "the single-most dangerous fault in the entire Bay Area."
The analysis came from the U.S. Geological Survey in Menlo Park, from Risk Management Solutions, a scientific and engineering firm in Newark, and from the Association of Bay Area Governments. Their view of the past and future was sobering.
Records and geologic trenching show that five major quakes struck along the Hayward Fault between 1315 and 1868 - an average of one every 140 years. The 140th anniversary of the last big one falls on Oct. 21.
Quakes don't follow timetables, of course, but "a repeat of 1868 is becoming increasingly likely with each passing year," said Survey seismologist Thomas Brocher. He is a leader of the "1868 Alliance," a consortium of quake experts and local officials working to persuade Bay Area residents to learn the elements of earthquake preparedness, to retrofit homes and businesses, to hold earthquake drills in every school and to keep emergency supplies on hand.
Brocher and Mary Lou Zoback, former chief scientist of the USGS earthquake hazards team and now vice president of Risk Management, noted that the Bay Area's $165 billion forecast for losses to residential and commercial buildings far exceeds the $141 billion damage to New Orleans buildings from Hurricane Katrina.
Many homes at risk
They pointed out that in New Orleans, 60 to 70 percent of total economic losses from the hurricane were uninsured, and in the Bay Area more than 95 percent of all homes and 85 percent of all commercial buildings have no insurance against earthquake damage.
According to Jeanne Perkins, a quake expert at the Association of Bay Area Governments, fewer than 40 percent of all Bay Area homes have been retrofitted to resist quake damage, and fewer than 10 percent have been strengthened enough to withstand "violent damage without becoming uninhabitable."
"When the Big One hits us, 27,000 homes in Oakland alone will be uninhabitable," said Sue Piper, a policy analyst for City Councilwoman Jean Quan. And most of them, she said, will be in houses occupied by low-income families who can ill afford the costs of retrofitting without some kind of assistance.
The biggest small-building hazard, all the experts agreed, will be from what they term "soft story buildings" - the kind where garages or storefronts occupy most of the ground floor and the heavier floors lie above, raising the odds of collapse. Houses like those, whose fragile underpinnings collapsed throughout San Francisco's Marina district when the Loma Prieta quake hit just over 18 years ago, should be a warning sign for every building owner to retrofit, Brocher said. Unreinforced corner buildings, he said, are the most dangerous.
The Loma Prieta temblor of October 1989 hit with a magnitude of 6.9. Sixty-four lives were lost, but the damage total was only $6 billion.
The loss figures from a magnitude 7 quake on the Hayward Fault will total $90 billion for residential buildings and their contents and $75 billion to commercial property, Zoback said.
Lifelines at risk
According to the risk management firm, half of all homes seriously damaged by the quake would be in Alameda County; 24 percent of damaged homes would be in Santa Clara County; 10 percent in Contra Costa; 7 percent in San Francisco; 5 percent in San Mateo County; and 4 percent in the remaining Bay Area counties.
Forty-three percent of all commercial property losses would be in Alameda County; 24 percent Santa Clara County; 8 percent in Contra Costa; 16 percent in San Francisco; 6 percent in San Mateo County; and 3 percent in the rest of the area.
Then there's the danger to lifelines - the roads, rail tracks and bridges that must carry ambulances, fire trucks and fleeing cars after the quake; the airports that are bound to be unusable; and the crucial power and gas lines whose damage costs haven't yet been figured in but could cost many lives, the risk experts agreed.
At least 1,100 Bay Area roads could be closed by a Hayward Fault quake, Perkins said - 900 in Alameda County alone.
In San Francisco, said Keith Knudsen of the national nonprofit Earthquake Engineering Research Institute, the downtown area south of Market, where well-engineered high-rises are rapidly filling the neighborhoods, would be particularly dangerous in a major quake because the low-lying filled land there is subject to liquefaction.
Those new buildings might well remain standing in the coming Hayward quake, he said, "but if the streets there settle by a couple of feet, those buildings will be isolated."
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