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Soil Liquefaction Due to Earthquakes

Earthquake motion can turn loosely packed, water-saturated soil to liquid—"liquefaction.” Liquefied soil loses its density and ultimately the ability to support roads, buried pipes, and, of course, houses.

The 1989 magnitude 6.9 Loma Prieta earthquake caused liquefaction, most severely in the Marina District of San Francisco. There, more than 30 buildings were damaged or destroyed, and gas lines were broken, igniting fires.

If liquefaction occurs on or near the homeowner's property, the house may sink by inches or several feet and be surrounded by or filled with liquefied soil. The California Governor's Office of Emergency Services MyHazards tool can help you identify geologic hazards near your house.

How to Prepare A House for Liquefaction

Retrofitting a house to withstand the effects of liquefaction typically involves improving the foundation, and the density of the soil around and under the house, achieved through soil excavation and compacting. The retrofitting method to prevent liquefaction damage varies from house to house, and homeowners considering a liquefaction retrofit should contact a geotechnical or civil engineer. The Earthquake Brace + Bolt program maintains a searchable database of California engineers.

For many homeowners, this type of retrofit can be cost-prohibitive. But earthquake insurance from a CEA participating residential insurer is available to help homeowners recover financially from earthquake liquefaction damage.