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Bracing for the next big earthquake

What would the Bay Area look like after the next big quake? The prospective picture is sobering, scientists say.

On the centennial of San Francisco's biggest natural disaster, the 1906 earthquake, many people are asking how a repeat rupture might affect the Bay Area today with at least 10 times the population.

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.

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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.

Scientists are largely concerned with the structural weaknesses of buildings in the Bay Area. Many three-story and higher buildings that include a bottom-floor garage are structurally weak, with a "soft" first story and more weight on top. Under the pressure of side-to-side shaking, those buildings tend to collapse, as many did in the 1906 quake and the Loma Priata quake in 1989. And of course, the lives of people on lower floors are threatened.

While many homes and buildings have been modernized or retrofitted with more stringent code, more than 50 percent of the buildings in San Francisco were built before 1940, without the benefit of modern building codes. What's more, about 80 percent of them were built before 1970, when really strong codes kicked in. Single family homes with one or two stories built after 1940 should be fine, researchers say, but multi-story buildings without retrofitting are vulnerable.

Most Bay Area bridges have been retrofitted, with some exception. The Bay Bridge, which partially collapsed in the 1989 earthquake, still is vulnerable on its east end, where it has yet to be updated. The on-ramps of the Golden Gate Bridge have been retrofitted, but the main span has yet to be modernized.

Scientists believe these buildings will stand strong: the Transamerica Building, the Legion of Honor, the Ferry Building and San Francisco City Hall, which has a state-of-the-art "base isolation" to withstand an earthquake. The major freeways have all been updated to the tune of $10 billion, thanks to the state government, but local-owned roads aren't prepared.

In the event of a major quake, tourism would likely be hit hard in the Bay Area, especially if San Francisco lost access to water for a long period.

In the Silicon Valley, home to the high-tech industry, the counties where the most damage is expected are Alameda, Santa Clara and San Mateo, which are all along the San Andreas fault.

The high-tech industry, one of the largest trades in the Bay Area, would likely suffer as a result. Scientists are unsure whether the Internet would be available in the area. Cell phones aren't expected to work because too many people will try to use them, and the repeater stations put up by wireless companies have not been hardened for strong shaking. Landlines, however, are more robust, but will likely be busy from too many people trying to use them.

According to representatives from Silicon Valley's chamber of commerce, many high-tech companies have existing back-up networks and software in other cities not only in preparation for an earthquake, but also previously from prepping for Y2K.

Yahoo, for example, said it has built redundancies across its network to offset any damage from an earthquake or other catastrophic event. Also, the company would attempt to use its site as a home base for victims.

"Yahoo would leverage its network as much as possible to provide critical information, help and resources for survivors," Yahoo spokeswoman Kelly Delaney wrote in an e-mail.

In terms of facilities, many tech company headquarters were built in recent decades and are up to code. "The tech companies tend to be really proactive about hardening facilities in their best financial interest," said USGS' Brocher.