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<br />D. Factors to Consider in the Selection of Design Earthquakes <br /> <br />The selection of design earthquakes should take into consideration the <br />geologic and seismic conditions in the region of the intended site, the <br />consequences of failure, the hazards associated with the facility, and <br />the physical requirements of the proposed engineering structure. The <br />following fac tors, ranging from regional to site specific, should be <br />considered in the se1ec tion of design earthquakes. These fac tors are <br />evaluated in the context of the current tectonic framework. The U.S. <br />Geological Survey Professional Paper 1114, entitled "Procedures for <br />Estimating Earthquake Ground Motions," 1980, by Walter W. Hays, is an <br />excellent source document for more detailed information. <br /> <br />'I <br /> <br />~ <br /> <br />Locating the project area on published information of source zones and <br />seismic risk areas will provide an initial indication of the level of <br />anticipated seismicity and a starting point for a more comprehensive <br />evaluation of site seismicity. <br /> <br />1. Regional Tectonic Setting <br /> <br />Information on regional geology and late Cenozoic tectonic history <br />is needed to assess the long-term seismic potential of the site as <br />part of the design earthquake selection process. This should <br />inc 1ude: <br /> <br />a. Identification of the physiographic province( s) within which <br />the project is located, e.g., Basin and Range, Lower <br />Mississippi Alluvial Plain, Appalachian Highlands, etc. <br /> <br />b. Location of the project area within its particular <br />seismotectonic province and relating its province with adjacent <br />provinces. <br /> <br />c. Description and identification of the principle tectonic events <br />and elements which charac terize the most recent tec tonic <br />activity. <br /> <br />d. Description of the regional geologic rock units and. structure <br />for consideration when evaluating seismic energy transmission, <br />effec ts, and duration. <br /> <br />2. Seismic History <br /> <br />Historical seismological information exists primarily within <br />governmental and academic references and the media record. The <br />National Earthquake Information Service of the U.S. Geological <br />Survey in Golden, Colorado, compi 1es source and magnitude <br />information for earthquake events. A thorough search of these <br />sources will provide information for a seismicity evaluation of the <br />site. Steps to follow and data to collect are: <br /> <br />a. Define the limits of the historical data search area <br />considering the boundaries of seismotectonic sources and <br />provinces of potential significance to the site. <br /> <br />-8- <br />