April 18, 2006 4:00 AM PDT
Bracing for the next big earthquake
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The prospective picture is sobering, say scientists from the U.S. Geological Survey, which is participating in the Earthquake Conference in San Francisco this week to commemorate the 100th anniversary of the catastrophe.
"The problem is that since 1906, the Bay Area has grown from about 700,000 to about 7 million (people)," said Tom Brocher, a seismologist at the USGS. "Our building codes are much more up to snuff for earthquake hazards, but the amount of damage today would be about the same as it was."
Among scientists' predictions are more than 5,000 deaths, 18,000 hospitalized, and as many as 160,000 flattened homes, rendering half a million people homeless. That likely includes damage to roads, water systems, cell phone networks and even the partially retrofitted Golden Gate Bridge. Silicon Valley, a largely rural area in 1906 but now America's high-tech mecca, would also be hard hit. All in all, researchers predict losses in the range of $60 billion to $300 billion.
Looking into the crystal ball isn't an exact science. Only in recent years have scientists had advanced tools to simulate ground shaking and potential destruction to a fault area, by using geographical and seismic data to tabulate 3D projections. Scientists also now increasingly draw on data from earth sensors and magnetometers, tools to measure changes in magnetic fields, to gather intelligence about earthquakes in the hopes of one day having an effective early warning system.
Still, natural disasters like the 1906 earthquake are, by nature, unexpected. This week's anniversary merely offers a reminder of the vulnerability of Northern California--and the world--to seismic activity that shapes the Earth, and what seem to be unnatural and violent shifts in weather.
Hurricane Katrina, for example, wreaked havoc on the Gulf Coast last year, flooding New Orleans and rendering millions homeless. Though residents were forewarned to evacuate, the scope of the damage and flooding couldn't be predicted--and the city of New Orleans is still struggling to rebuild itself. The tsunami in the Indian Ocean also took Southeast Asia by surprise.
Video: Preparation for the next major quake
USGS examines expected damage to roads, problems of recovery after major Silicon Valley or San Francisco earthquake.
All eyes are on the great San Francisco earthquake on Tuesday, when 100 years ago a quake with a magnitude of between 7.8 and 7.9 rocked the Bay Area 300 miles along the San Andreas fault, from Alameda all the way up to Cape Mendocino.
The earth moved about two feet in a horizontal direction. Although the quake occurred roughly 10 miles below the surface of the earth, it took only about three seconds for the ground to begin shaking. The leading edge of the quake--the first waves emanating from it--traveled at 14,000 miles per hour, while the shaking behind it traveled at 8,000 miles per hour.
Most of the destruction in the 1906 earthquake was concentrated in San Francisco, the Bay Area's nexus of population, compared with the other, mostly rural, areas at the time. Roughly 3,000 people died in flattened homes or by the out-of-control fire that followed, and as many as 225,000 were made homeless, or more than a third of the population. (Another 500 people lost their lives in outlying areas.) The homeless were living in tent camps in Golden Gate Park and Washington Square Park, among other areas.
Half the buildings in San Francisco were lost, most of which burned in the fire.
Scientists expect many of the areas hit hard along the San Andreas fault in 1906 to be vulnerable to another major quake within 30 years.
The USGS predicts there's a 62 percent chance of a magnitude 6.7 earthquake or larger in the Bay Area in the next 30 years, or "a very damaging earthquake." For the San Andreas, which was the fault responsible for the 1906 quake, there's a 21 percent chance it will occur in the next 30 years. But a magnitude of that quake occurs every 200 to 350 years, and the Bay Area is, at best, only halfway through the cycle.
A program developed by the Federal Emergency Management Agency (FEMA) helps the USGS calculate the levels of losses expected in the event of strong shaking caused by any of the seven deadly faults in the Bay Area. Those faults include the San Andreas, Calaveras, Green Valley, Grenvele, San Gregorio and Mt. Diablo.
If and when a 1906 repeat does occur, predictions show that roughly 37,000 office buildings would be destroyed in areas concentrated along the fault zones of San Francisco, San Mateo, Santa Clara County, Alameda and Oakland. Along with an estimated 160,000 homes, the damage in building units would be about 10 percent of the total 2.1 million buildings in the Bay Area.
FEMA estimates the damage to be roughly $60 billion, with more than 50 percent of that in housing losses. Comparatively, the Association of Bay Area Governments predicts it more in the range of $100 billion. Jayanta Guin, vice president of research at AIR Worldwide, a risk-modeling company, projects total property losses of $300 billion, or about $80 billion in insured losses.
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