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Soil Liquefaction for Insurance Underwriting

June 26, 2012
Soil Liquefaction Mapping

PropertyEDGE Soil Liquefaction Mapping

Are you insuring risks in an earthquake zone? Do you know all you should about the impact an earthquake can have on property? Knowing your property’s distance from a fault line is important, but it doesn’t tell you everything when it comes to determining the risk of damage during an earthquake. Soil liquefaction maps can help give you a more complete picture of your risk.

Liquefaction is a process that occurs when sediment becomes saturated with water, loses strength, and acts like a liquid. Soil deposits are made up of individual soil particles that are in constant contact with each other. The weight of each particle exerts force on its neighboring particles, holding them in place and creating the soil’s strength. Soil liquefaction occurs during earthquakes because shaking increases the groundwater pressure surrounding the soil particles. The packed soil becomes saturated and the particles lose contact with each other, compromising its strength. As a result, the soil softens and shifts. This can result in building foundations sinking, retaining walls breaking, and structures buckling. Some soils are more susceptible than others, such as loose, sandy soil or those located at or below sea level.

It’s best to address the issue of liquefaction susceptibility before building, but if a structure already exists, there are still measures that can be taken to reduce the likelihood of damage during an earthquake. Structures can be retrofitted and reinforced to reduce the impact of movement caused by liquefaction, and soil under and around structures can be improved through densification, solidification, drainage, dewatering, and reinforcement.

All buildings can be strengthened by bracing, reinforcing masonry, sheer plating (adding plates of plywood to stud walls is the most common), and bolting walls to foundations. In addition, securing heaving objects from falling (bookshelves, computers, etc.) is always a good idea.

Soil liquefaction maps can help you to determine the level of risk for liquefaction at the exact location of your property. Liquefaction maps for Washington State are now available through WSRB‘s PropertyEDGE™ software. For more information, call or email Tracy Skinner at 206.273.7146.

Do you have questions about soil liquefaction or PropertyEDGE? Leave us a comment below.


Article by: April LaRita Green

Source: University of Washington

2 Comments leave one →
  1. June 26, 2012 3:49 pm

    Excellent article April. Thank you for sharing.

    • June 27, 2012 9:02 pm

      Thanks Mark. We’re glad you found it interesting.

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