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Earthquakes <br />Earthquakes: Description <br />According to the 2013 State of Texas Hazard Mitigation Plan Update, earthquakes <br />are defined as a shaking or trembling of the earth that is volcanic or tectonic in <br />origin. <br />Earthquakes: Extent Scale <br />The magnitude of an earthquake can be measured with the USGS Mercalli Scale and <br />Peak Ground Acceleration Comparison in Table 2.27. <br />Risk Assessment <br />Perceived Estimated <br />Potential Structure Damage <br />Mercalli ScaleShakingPGA* <br />Resistant BuildingsVulnerable Buildings(%g) <br />INot FeltNoneNone<0.17% <br />II to IIIWeakNoneNone0.17% - 1.4% <br />IVLightNoneNone1.4% - 3.9% <br />VModerateVery LightLight3.9% - 9.2% <br />VIStrongLightModerate9.2% - 18% <br />VIIVery StrongModerateModerate/Heavy18% - 34% <br />VIIISevereModerate/HeavyHeavy34% - 65% <br />IXViolentHeavyVery Heavy65% - 124% <br />X to XIIExtremeVery HeavyVery Heavy>124% <br />*PGA measured in percent of g, where g is the acceleration of gravity <br />Figure 2.4 shows the USGS 10% Probability of Exceedance in 50-Year Map of Peak Ground Acceleration <br />and the respective location of the HMP update areas. The FEMA How-To Guidance, Understanding Your <br />Jurisdiction-specific data for location, previous occurrences, extent, probability, impact, and vulnerability <br />are found in jurisdiction annexes. <br />56 <br /> <br />