Item 26 - Adoption of the City of Santa Ana Emergency Operations Plan

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City of Santa Ana Emergency Operations Plan Part I Basic Plan thousands of people temporarily homeless. Of the 66,500 buildings inspected, nearly 4,000 were severely damaged and over 11,000 were moderately damaged. Several collapsed bridges and overpasses created commuter havoc on the freeway system. Extensive damage was caused by ground shaking, but earthquake -triggered liquefaction and dozens of fires caused additional severe damage. This extremely strong ground motion felt in large portions of Los Angeles County, and in Orange County as well, resulted in record economic losses including direct and indirect economic losses of approximately $46 billion. Even so, this earthquake occurred in the very early morning hours of a national holiday. Many collapsed buildings were unoccupied, schools and most businesses were not yet open and freeways were sparsely traveled. This factor considerably reduced the impacts of this earthquake. Earthquake Hazards Ground shaking, ground failure and tsunami are the specific hazards associated with earthquakes. The severity of these hazards depends on several factors, including soil and slope conditions, proximity to the fault, earthquake magnitude, and the type of earthquake. Ground Shaking - Ground shaking is the motion felt on the earth's surface caused by seismic waves generated by the earthquake. It is the primary cause of earthquake damage, producing 98% of structural and nonstructural (contents) damage. The strength of ground shaking depends on the magnitude of the earthquake, the type of fault, and distance from the epicenter where the earthquake originates. Additionally, buildings constructed on loose, poorly consolidated or soft soils will typically see more damage than buildings on consolidated soils and bedrock. In some cases, ground shaking and the associated damage may actually be more severe in places farther from the fault than nearer locations, due to differences in soil consistency and amplification of the seismic waves as they travel through the earth. This was the case with the 1989 Loma Prieta Earthquake, whose epicenter was in the Santa Cruz Mountains but some of the most severe shaking and damage occurred about 60 miles to the north in the San Francisco Bay Area. Ground Failure - Ground failures can include surface rupture, liquefaction and landslides. Surface Rupture - The sliding movement of the earth on either side of a fault is called fault rupture. Fault rupture begins below the earth's surface but in a powerful enough earthquake, may actually travel all the way to the ground surface, creating a visible crack or separation of the ground surface. This can result in massive damage to any structures built above the rupture, as well as significant damage to roadways, utility lines or other structures located on the rupture. With no known active faults in the City of Santa Ana, the risk of surface rupture occurring in the City of Santa Ana is believed to be minimal. Liquefaction - Liquefaction occurs when soft, loose or water -saturated soil settles suddenly during earthquake shaking. The soil converts to a fluid -like substance, causing it to lose the strength to support the weight of buildings or other structures, and these structures will sink or topple over. Many communities in Southern California, including portions of Santa Ana, are built on floodplains or ancient river or lake bottoms and have loose, sandy soil. The Figure below shows the areas of Orange County that may be susceptible to liquefaction. See also the California Geological Survey website at http:Hgmw.consrv.ca. ov/shmp/html/pdf maps_so.html, where the California Geological Survey has identified areas most vulnerable to liquefaction. 36