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<br /> <br />p(R=r~lrn;) = probability that given the occurrence of an earthquake ~~f magnitude <br />' m; on source n, r~ is the closest distance increment frorn the rupture <br />surface to the site; <br />p(Z~zlm;,r~ = probability that given an earthquake of magnitude m; at a distance <br />of rp the ground motion exceeds the specified level z. <br />The calculations were made using our computer programs XCEED anal EXPOSE <br />(Woodwazd-Clyde Consultants, 1979). <br />Seismic Source Characterization <br />Two types of earthquake sources aze chazacterized in this seismic hazard analysis: (1) faults <br />and (2) areal source zones. Faults are modeled as three-dimensional fault surfacf:s and details <br />of their behavior are incorporated into the source characterization. Areal source zones are <br />regions where earthquakes are assumed to occur randomly. Seismic sources arc modeled in <br />the hazard analysis in terms of maYirnum magnitude, geometry, and earthquake recuarence. <br />The geometric source parameters for faults include fault location, segmentation. model, dip, <br />and thickness of the seismogenic zone. The recurrence parameters include recurrence model <br />(exponential and characteristic), recurrence rate (slip rate or average recurrence: interval for <br />the maximum event on a fault or number of events over the minimum magnitude for a source <br />zone), and slope of the recurrence curve (b-value). Clearly, the geometry and recurrence are <br />not totally independent. For example, if a fault is modeled with several small segments <br />t instead of lazge segments, the maximum magnitude is lower, and a given slip rate requires <br />many more small earthquakes to accommodate a cumulative seismic moment. <br />^ For areal sources, only the maximum magnitude, azeas and recurrence need tcl be defined. <br />' Uncertainties in the source parameters are included in the hazard model usin;; logic trees <br />(Figure 1). In the logic tree approach, discrete values of the source input paz<Imeters have <br />been included along with~our estimate of the likelihood that the discrete value nepresents the <br />actual value. Generally all input parameters have been represented by three values: a central <br />value, which represents our best estimate of the pazameter, and lower and higher values to <br />' represent the distribution around the best estimate. <br />H:ICONIRACT274561.DUR1 4 M0709951609 <br />