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<br />displacement, and velocity against period or frequency. <br />The response spectra of the ground motion at the site can be <br />defined by using site-independent or site-dependent procedures. <br /> <br />a. Site-Independent Response Spectra <br /> <br />Site-independent response spectra are based on the use of <br />standard spec trum shapes. The standard spec trum shapes are <br />site-independent because they are based on earthquake <br />ground motion rec ord s from a wide range of geologic, <br />seismological, and local site conditions. For example, the <br />ground motion records represent different earthquake <br />magnitudes, soil (shallow and deep) sites, rock (various <br />geological types) sites, different distances from the <br />epicenter, etc. <br /> <br />There have been several studies published defining site- <br />independent response spectra. The basic differences in <br />these studies have been in the number of earthquake records <br />used and the statistical treatment of the records. <br /> <br />Before u sing pub lished site-independent response spec tra, a <br />determination should be made tha t they are applicable to <br />the site. In order to do this, thorough evaluations should <br />be made on how they were developed to ensure proper and <br />consistent use. For example, some published site- <br />independent response spectra shapes correspond to the <br />average of the earthquake ground motion records used to <br />develop the shape, while some are based on the 84th <br />percentile shape. Use of these spec tra without <br />understanding their development can lead to improper <br />application. <br /> <br />Additional studies can be performed to determine site- <br />independent response spectra, but published studies should <br />be evaluated to avoid unnecessary work. The published <br />studies cover a broad range of conditions. If the <br />pub lished site-independent re sp on se spec trs are not <br />applicable, then development of site-dependent response <br />spec tra would be the best approach to pursue. <br /> <br />b. Site-Dependent Re sponse Spec tra <br /> <br />Si te-dependent re sponse spec tra can be deve loped for si te <br />specific conditions using earthquake ground motion records <br />which were recorded under similar site-matched conditions. <br />The ability to develop site-dependent spec tra is based on <br />finding relevant ground motion records which permit a <br />meaningful statistical evaluation. <br /> <br />The site-dependent characteristics which should be <br />considered are the foundation conditions (soil and rock, <br />deep or shallow soil, rock type, etc.), magnitude of the <br /> <br />-15- <br />