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<br />Professor C.A. Cornell (1968) developed the probabilistic seismic <br />hazard assessment methodology to provide a more realistic assessment <br />of earthquake hazards and to account for uncertainties that aze an <br />inherent part of geological and seismological interpretations. The <br />probabilistic method eschews the single value, scenario-like model in <br />favor of multivalued models incorporating uncertainty (Reiter, 1990). <br />The assessment includes the effects of all earthquakes likely to affect <br />the site, and alternative interpretations and related uncertainties can be <br />easily incorporated. The probability that a given level of ground <br />motion will occur within a given time period is an important product <br />of the method. The results of probabilistic analyses are commonly <br />presented graphically either as a probability of non-exceedance for <br />given time periods or as an annual probability of exceedance versus <br />peak ground acceleration (or other parameter) for all sources contribut- <br />ing to hazard at a given site. <br />For this study, we used the computer program SEISRISK III by <br />Bender and Perkins (1987). The program requires the following <br />inputs: (1) definition of seismic source zones either azeal sources <br />(seismotectonic regions) or line sources (faults) including location, <br />geometry, earthquake recurrence relations, and maximum magnitudes; <br />(2) an appropriate attenuation relation; and (3) desired probabilities of <br />non-exceedance. Detailed discussion of the program is contained in <br />Bender and Perkins (1987). Specific inputs for this study are discussed <br />below. <br />7.1 SEISMIC SOURCES <br />Probabilistic assessment of seismic hazards requires consideration of <br />potential earthquake source zones, either identifiable seismogenic <br />faults or lazger areas with common seismogenic characteristics. Once <br />source zones have been identified, recurrence relations can be estab- <br />lished and maximum earthquakes can be assigned based on synthesis <br />of geologic and seismologic data. In the following sections, we <br />discuss identification of fault and areal source zones for use in the <br />PSHA. Fault and areal source zones used in the PSHA for Trout <br />Creek dam are illustrated on Figure 1. <br />25 <br />