2019_KittitasCountyHMP_Volume 1_For Adoption

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CHAPTER 10. EARTHQUAKE 10-24 Category Not Felt to Weak Light to Moderate Strong to Very Strong Severe to Violent Extreme Total 0 20 35 1 0 10.6.4 Environment The environment vulnerable to earthquake hazard is the same as the environment exposed to the hazard. 10.7. FUTURE TRENDS IN DEVELOPMENT The land use elements of the comprehensive plans adopted by the municipal planning partners provide a long-range guide to the physical development of the planning area and its urban growth area. As one of the faster growing counties in Washington, Kittitas County and its planning partners will need to manage growth in a way that accounts for impacts from potential earthquakes. With tools such as the Washington State Building Code and local critical areas ordinances that define seismic hazard areas, the planning partners are prepared to deal with future growth. 10.8. SCENARIO Any seismic activity of Magnitude 6.0 or greater on faults within the planning area would have significant impacts. The seismic event likely to have the largest impact is a Magnitude 6.8 or greater event on the Cle Elum fault. Potential warning systems could give 40 seconds’ notice that a major earthquake is about to occur; this would not provide adequate time for preparation. Earthquakes of this magnitude or higher would lead to significant structural failure of property on unstable soils. With the abundance of floodplain within the planning area, liquefaction impacts in these areas could be widespread. Un -engineered canal embankments would likely fail, representing a loss of critical infrastructure. The structural integrity of the numerous earthen dams within the planning area could be jeopardized as well. These events could cause secondary hazards, including landslides and mudslides. River valley hydraulic-fill sediment areas are also vulnerable to slope failure, often as a result of loss of cohesion in clay-rich soils. Soil liquefaction would occur in water-saturated sands, silts or gravelly soils. 10.9. ISSUES Important issues associated with an earthquake include but are not limited to the following: • Approximately 42 percent of the planning area’s building stock was built prior to 1975, when seismic provisions became uniformly applied through building codes. • Critical facility owners should be encouraged to create or enhance continuity of operations plans using the information on risk and vulnerability contained in this plan. • Geotechnical standards should be established that take into account the probable impacts from earthquakes in the design and construction of new or enhanced facilities. • Major infrastructure crossing vulnerable soils, such as roads, bridges and railroads, is at risk. • Landslides could have a widespread effect on the city and its surrounding areas. • The county has over 330 miles of canals that were not constructed to engineering standards. The structural integrity of these facilities as it pertains to seismic impacts is not known. • Until additional data on the impacts of events typical for this region are developed, non- structural retrofitting techniques should be considered and promoted by the partnership.