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<br /> <br />5.2. Liquefaction <br />Soil that is loose, sandy, silty, or saturated with water can result in soil liquefaction if it is <br />shaken intensely for an extended period. When ground liquefies in an earthquake, it <br />behaves like a liquid and may sink, spread, or erupt in sand boils. This can cause pipes to <br />break, roads and airport runways to buckle, and building foundations to be damaged. <br />Liquefaction can only occur under certain circumstances:12 <br />Loose Soils The soils must be loose, such as uncompacted or unconsolidated sand <br />and silt without much clay. This happens most often in the Bay Area <br />along the Bay shoreline, near creeks or other waterways, on dry creek <br />beds, and in areas of man-made fill, such as the Marina District in San <br />Francisco or parts of Alameda. <br />Soggy Soils The sand and silt must be soggy and saturated with water due to a <br />high water table. <br />Ground Shaking The ground must be shaken long and hard enough by the earthquake <br />to trigger liquefaction. <br />Liquefaction may not necessarily occur even if all three conditions are present. <br />Additionally, if liquefaction does occur, the ground may not move enough to have <br />significant impact on the built environment. As with ground shaking, several types of maps <br />depict liquefaction potential. Liquefaction susceptibility maps show areas with soil types <br />known to have the potential to liquefy with intense shaking. <br />Unless areas of liquefaction susceptibility are subject to significant ground shaking, they <br />are not likely to liquefy. Liquefaction hazard maps express where the ground is both <br />susceptible to liquefaction, and where the ground is likely to be shaken long and intensely <br />in an earthquake. In 2015, ABAG produced maps that combine liquefaction susceptibility <br />with USGS-generated earthquake scenario maps to identify areas where there is a <br />significant hazard of liquefaction. Figure 5 is a representative example which shows the <br />liquefaction potential in a M7.0 Hayward earthquake. The map combines the liquefaction <br />susceptibility and Hayward shaking information into a scenario-based liquefaction <br />potential map. <br /> <br /> <br /> <br /> <br />12 Perkins, J.B., (2001)