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Is Your Home In A Liquefaction Zone

 

The California state government has created a website which will give you a simple description of the liquefaction hazard and other natural hazards for any property. Check out at the MyHazards website and select the “Earthquake Risk” tab to find out if your home is in a Liquefaction Zone Area

 

Understanding Liquefaction Zones

 

The ABAG report "The REAL dirt on Liquefaction" and web site provides the following quote:

"The 1989 Loma Prieta earthquake caused a total of $5.9 billion in property damage. Most of the damage was due to ground shaking. However, approximately $100 million of that (1.6%) was due to liquefaction."

 

The Loma Prieta earthquake occurred at the end of the dry season in October of a relatively dry year.

 

 

Three factors are required for liquefaction to occur

 

  1. loose, granular sediment - typically beach and stream deposits or land fill.

  2. saturation of the sediment by ground water - water fills the spaces between sand and silt grains

  3. strong shaking - all portions of the San Francisco Bay Area have the potential for susceptible areas to be shaken hard enough for liquefaction to occur.

 

 

Susceptible Areas

 

The San Francisco Bay Area has 77 square miles of land made through fill being poured into the bay and wetlands since 1845. This along with much of the natural land at low elevations are susceptible to liquefaction. Loose sediment along existing and filled streams may also be susceptible. The pressing question is how large an area will be impacted? In San Jose the area extends from the San Francisco Bay to approximately Stevens Creek Blvd. In Palo Alto most of the area between the bay and Alma Street is impacted.

The Santa Clara County Government Geologic Hazard Maps provide excellent detail. A screen shot of one for Palo Alto is shown below.

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