Repeat of Quake Of 1906 Could Be Even More Deadly
Monday, April 17, 2006
Timed to coincide with the 100th anniversary of the catastrophic 1906 San Francisco earthquake this week, researchers have calculated the possible death and destruction that could occur if another temblor of equal strength struck the Bay Area today.
The worst-case scenario? As many as 3,400 dead, mostly crushed by buildings; up to 700,000 people displaced or homeless; 130,000 structures extensively damaged or destroyed; and immediate losses exceeding $125 billion -- a forecast that rivals the mayhem unleashed by Hurricane Katrina and the breaching of the New Orleans levees.
The new study, titled "When the Big One Strikes Again," uses the best estimates of the size and strength of the April 18, 1906, event, a magnitude-7.9 quake and ensuing firestorm that killed more than 3,000 people and destroyed vast swaths of San Francisco.
The computer simulation study, to be released today in San Francisco at the beginning of the largest-ever conference about earthquakes, concludes that a repeat of the 1906 quake could be more devastating than the original because the region is now more densely settled, the value of the real estate is much higher and the population is 10 times larger.
The 1906 earthquake ran along 300 miles of the San Andreas Fault and was felt in an area that today has 10 million residents and 3.5 million buildings valued at $1 trillion. Most of the people and property are within 25 miles of the fault line.
Mary Lou Zoback, a senior research scientist with the United States Geological Survey in Menlo Park, Calif., reviewed the study and endorses its forecast. She says what leaps out at her is how vulnerable the urban core of the Bay Area is -- the cities of San Francisco, Berkeley and Oakland -- because so many of the residents live in apartments and houses built before building codes were tightened in 1970. (And because many units are rent-controlled apartments, she says, landlords have few incentives to seismic retrofit.)
"When you're talking, potentially, about 400,000 to 700,000 people homeless," Zoback said, "where are they going to go, when roads will be impassable, when the major north-south freeways are damaged, when the east-west tunnels are closed due to landslides? When, even if the bridges stand up, you may not be able to get to them?"
The study was conducted by structural engineer Charles Kircher and his colleagues, using 2,000 census tracts, which detail the types of buildings; their age, size and value; and the population in each tract. The team also tried to identify how many of the buildings were built with the most vulnerable materials and weaker construction methods, such as unreinforced masonry and "tuck under" garage apartments, which Kircher called "killer buildings."
Perhaps for good reason. A building's ability to withstand violent shaking is fairly well understood by engineers. Although the dangerous structures represent only 5 percent of the region's building stock, their collapse during the simulated Big One accounted for half of the death toll.
Kircher and his team ran computer models simulating the ground motion of the 1906 earthquake occurring today at 2 a.m. and 2 p.m. A daytime quake is considered more deadly because more people would be at work around the killer buildings, whereas during a nighttime event people would be at home in their beds. The simulation predicts between 800 and 3,400 deaths, depending on time and other variables. The model does not identify which individual buildings might fall, but instead gives averages over a census tract of the likely extent of the damage.
"I feel confident that our estimates are within the ballpark," said Kircher, whose study was sponsored by several scientific societies and the 100th Anniversary Earthquake Conference. For a comparison, Kircher said, the 1995 earthquake in Kobe, Japan, killed more than 5,000 people, and most deaths were building-related. But Kircher cautions that his study is just computer models, not destiny.
The semi-apocalyptic scenario sounds about right to Richard Eisner, coastal regional administrator for California Gov. Arnold Schwarzenegger's Office of Emergency Services.
"In 1906, San Francisco was the largest city west of the Rockies. We had 400,000 people in the city," Eisner said. "Today we have 7 million in the Bay Area. And the consequences of a disaster of this magnitude in an urban area are significant."
Eisner's office focuses less on the short-term survival of residents in a massive earthquake -- that's the province of local governments -- and more on the long-term consequences of a disaster.
"The recovery of 1906 lasted for a decade," he points out. "We are, all of us, observing and participating in the recovery of the Gulf Coast. And the level of complexity of that recovery is what we need to be preparing for."
Seismologists generally agree that a repeat of a 1906-size earthquake is inevitable, though when and where along the fault are unknown. In 2002, the U.S. Geological Survey reported a 62 percent chance of a magnitude-6.7 earthquake or greater hitting the Bay Area within 30 years. That would be about the size of the 1994 Northridge quake in Los Angeles, which killed 57 people and caused $20 billion in damage. An earthquake the size of the 1906 event would be far more destructive, but researchers say such quakes are relatively rare. Zoback of the Geological Survey says a Big One appears to occur every 200 to 250 years.
Chris Poland, chairman of the 100th Anniversary Earthquake Conference, sees the centennial as a good opportunity for San Franciscans to evaluate what preparations they could still make for a severe quake. It's all too easy, he says, to put one's head in the sand.
"I've got to confess to you, I hear about bird flu and I think, am I going to worry about bird flu? I don't think so," Poland said. "That's how we deal with low-probability, high-consequence events."
"It's sobering to think of 250,000 people out of their homes. Some will be out permanently," Poland said. "There hasn't been a lot of concern given to the condition of the buildings themselves after the earthquake. Building officials are responsible only for public safety, not for protecting assets," so many homes that do not collapse immediately will still be uninhabitable, he says.
As for those buildings that engineers already know will collapse, "that's really where the danger is," he said, yet many people underestimate their risk. "You know if you're behind the levee," Poland said, referring to the New Orleans flooding. "I really think people need to know what kind of condition their building is in."
And where would a few hundred thousand people go, if they could not reenter their homes? Poland would also like to see officials focus on evacuation plans.
"How do we take care of vulnerable populations who can't move themselves? Emergency services is working on that," Poland said. "I hope it's going to be better than just getting a bunch of buses and shipping them out across the western United States."
Staff writer Sonya Geis contributed to this report.