April 18, 2006 4:00 AM PDT

Bracing for the next big earthquake

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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.

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2007 Bay Area Catastrophic Earthquake, Inevitable
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