New maps reveal South Bay quake risks


According to new seismic maps done by the U.S. Geological Survey, the Highway 87-101 interchange is one of the high-risk locations for earthquake liquefaction -- but the good news about this South Bay interchange -- Caltrans built it in 2005 using state-of-the-art construction - so it should hold up well.

New research by the USGS shows that parts of Santa Clara Valley have a high-risk of liquefaction -- which happens when damp sand turns liquid-like during an earthquake. Maps were made based on 100 borings in valley soil. And they reveal the most danger lies along San Jose's Guadalupe River and Coyote Creek flood plains.

If a major earthquake, like a 7.8 hits along the San Andreas fault, then the USGS calculates that homes and businesses nearby these two waterways would be at 30 to 40 percent risk of liquefaction -- some locations most at-risk could include Cisco Systems, the Highway 87-101 interchange, the San Jose Mercury News facility, and part of the Mineta San Jose International Airport.

Businesses, like Cisco and the Mercury News, say they're still reviewing the USGS report to assess their seismic risks. It's still too early to know whether these new findings could impact earthquake insurance rates for property owners. Others, like the airport, say the construction there already takes into account the sandy soils, and airport structures have been stabilized with large sunken concrete pilings.

This new research about earthquake-induced liquefaction in Santa Clara Valley will be published next month's issue of the 'Bulletin of the Seismological Society of America'.

Buildings on this type of soil can be also be made safer for example, by solidifying the sand through injections of grout and other chemicals. The USGS has made available the new maps on its website, so property owners can plug in their address and zoom to street level to check out their statistical risk for liquefaction.

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