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<br />~J <br />The average return time for the characteristic or maximum magnitude earthquake defines the <br />high magnitude (low likelihood) end of the recurrence curve. When combined with the <br />' relative frequency of different magnitude events from the recurrence model, the recurrence <br />curve is established. <br />' Attenuation Relationshias <br />To characterize the ground motions at a specified site as a result of the seismic sources <br />considered in the probabilistic seismic hazazd analysis, empirical attenuation relationships for <br />peak horizontal acceleration are used. Such relationships have been developed from strong <br />motion records from past earthquakes. The strong motion data typically are analyzed <br />' statistically in a regression analysis to develop relationships between the ground motion value, <br />distance from the earthquake to the recording station, and magnitude of the earthquake. <br />' Other pazameters used in these relationships often include the style of faulting and the soil <br />conditions at the recording site. <br />Given a maximum magnitude and source-to-site distance for specific seisnuc sources, <br />' published attenuation relationships can be used to define the median, and t one standazd <br />deviation (16th and 84th percentile) ground motions for a site. The attenuation relationships <br />used in this study were selected on the basis of the appropriateness of the site conditions and <br />~' tectonic environment for which they were developed. The relationships selected generally <br />represent recent efforts in modeling strong ground motion on the basis of empirical data, <br />although many of the relationships employ theoretical arguments to constrain some of the <br />model pazameters. <br /> <br /> <br />~' <br /> <br /> H:\CONiRACn23C561DUN7 ~] M0309951609 <br />