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<br /> <br />Earthquake <br /> <br />planning. After thorough review of the studies, professional organizations of engineers update the seismic-risk <br />maps and seismic design requirements contained in building codes (Brown et al., 2001). The USGS updated the <br />National Seismic Hazard Maps in 2018. New seismic, geologic, and geodetic information on earthquake rates and <br />associated ground shaking were incorporated into these revised maps. The 2018 map, shown in Figure 10-1, <br />represents the best available data as determined by the USGS. <br /> <br />Source: USGS, 2021 <br /> <br /> Figure 10-1. Peak Acceleration (%g) with 2% Probability of Exceedance in 50 Years <br /> <br /> <br />10.1.7 Liquefaction and Soil Types <br />Soil liquefaction occurs when water-saturated sands, silts or gravelly soils are shaken so violently that the <br />individual grains lose contact with one another and float freely in the water, turning the ground into a pudding- <br />like liquid. Building and road foundations lose load-bearing strength and may sink into what was previously solid <br />ground. Unless properly secured, hazardous materials can be released, causing significant damage to the <br />environment and people. <br /> <br />A program called the National Earthquake Hazard Reduction Program (NEHRP) creates maps based on soil <br />characteristics to help identify locations subject to liquefaction. NEHRP soil types define the locations that will be <br />significantly impacted by an earthquake. Table 10-2 summarizes NEHRP soil classifications. NEHRP Soils B and <br />C typically can sustain ground shaking without much effect, dependent on the earthquake magnitude. The areas <br />that are commonly most affected by ground shaking have NEHRP Soils D, E and F. In general, these areas are <br />also most susceptible to liquefaction. The areas that are most commonly affected by ground shaking have NEHRP <br />Soils D, E and F. <br /> <br /> <br /> <br /> <br /> <br />10-5