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2025 Hazard Mitigation Plan <br />Kittitas County, Washington <br /> <br /> <br />Chapter 4: Hazard Identification and Risk Assessment 110 <br />Table 4-50. Modified Mercalli Scale vs. Richter Scale <br /> <br />Earthquakes can trigger other types of ground failures, which could contribute to the damage. These <br />include flow failures, landslides, and liquefaction. Liquefaction is not a type of ground failure; however, it <br />is a physical process that occurs when shaking can mix groundwater and soil, liquefying and weakening <br />the ground that supports buildings and severing utility lines. This is a problem in floodplains where the <br />water table is relatively high, and the soil is more susceptible to liquefaction.134F <br />134 <br /> <br />The National Earthquake Hazards Reduction Program (NEHRP) defined six (6) different site <br />classifications, based on the type of soil and rock in the area, and their shear-wave velocity. NEHRP soil <br />type A (hard rock), B (rock), and C (very dense soil and soft rock) typically can sustain low magnitude <br />ground shaking without much effect. On the other hand, NEHRP soil types D (stiff soil), E (soft clay soil), <br />and F (could contain different types of soils, requiring site-specific evaluations) are most affected by <br />ground shaking making these areas more susceptible to liquefaction.135F <br />135 Figure 4-12 shows the NEHRP <br />soil classifications present in Kittitas County. <br /> <br /> <br />134 United States Geological Survey. (n.d.). What are the Effects of Earthquakes? Retrieved from: <br />https://www.usgs.gov/programs/earthquake-hazards/what-are-effects-earthquakes. <br />135 Nolan, J. (2022). The Effects of Soil Type on Earthquake Damage. Retrieved from <br />https://www1.wsrb.com/blog/the-effects-of-soil-type-on-earthquake-damage. <br />Intensity Effects <br />Richter <br />Scale <br />(approximate) <br />I. Instrumental Not felt. 1 – 2 <br />II. Just Perceptible Felt by only a few people, especially on upper floors of tall buildings. 3 <br />III. Slight Felt by people lying down, seated on a hard surface, or in the upper <br />stories of tall buildings. 3.5 <br />IV. Perceptible Felt indoors by many, by few outside; dishes and windows rattle. 4 <br />V. Rather Strong Generally felt by everyone; sleeping people may be awakened. 4.5 <br />VI. Strong Trees sway, chandeliers swing, bells ring, some damage from falling <br />object. 5 <br />VII. Very Strong General alarm; walls and plaster crack. 5.5 <br />VIII. Destructive Felt in moving vehicles; chimneys collapse; poorly constructed buildings <br />seriously damaged. 6 <br />IX. Ruinous Some houses collapse; pipes break. 6.5 <br />X. Disastrous Obvious ground cracks; railroad tracks bent; some landslides on steep <br />hillsides. 7 <br />XI. Very Disastrous Few buildings survive; bridges damaged or destroyed; all services <br />interrupted (electrical, water, sewage, railroad; severe landslides). 7.5 <br />XII. Catastrophic Total destruction; objects thrown into the air; river courses and <br />topography altered. 8