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SECT NFOUR Seismic Hazard Inputs <br /> value is recommended as an upper-bound velocity for use in the NGA-West2 models by most of <br /> the developers. Recent research (e.g., Ktenidou and Abrahamson, 2016) indicate that using the <br /> NGA-West2 models for the hard rock at this site may be unconservative for short period ranges <br /> (less than 0.2 seconds). It is assumed that the tailings dams are not sensitive to such short-period <br /> ground motions. <br /> Other input parameters include Zi.o,the depth of a Vs of 1.0 km/sec and Z2.5,the depth to a Vs of <br /> 2.5 km/sec. Both parameters were used by some of the developers as proxies for basin effects. <br /> Z,o is used by Chiou and Youngs (2014)and Abrahamson et al. (2014) and Z2,5 is only used in <br /> one model, Campbell and Bozorgnia (2014). Due to the lack of site-specific data, the default <br /> value of Z2 5 based on the Vs30 from equations provided by the developers was used in the <br /> PSHA. Other parameters such as depth to the top of rupture (zero for all faults that intersect the <br /> surface unless specified otherwise), dip angle, rupture width, and aspect ratio were specified for <br /> each fault or calculated within the PSHA code. <br /> As noted by Al Atik and Youngs (2014) the development of the NGA-West2 models was a <br /> collaborative effort with many interactions and exchanges of ideas among the developers and the <br /> developers indicated that an additional epistemic uncertainty needs to be incorporated into the <br /> median ground motions in order to more fully represent an appropriate level of epistemic <br /> uncertainty. Hence, for each of the four NGA-West2 models an additional epistemic uncertainty <br /> on the median ground motion was included. The three-point distribution and model of Al Atik <br /> and Youngs (2014) was applied (Figure 4). The model is a function of magnitude, style of <br /> faulting,and spectral period. <br /> We did examine recent ground motion models developed for Europe, which are based on <br /> datasets which contain more normal faulting events. Specifically, we examined the models of <br /> Akkar, et al. (2014)and Bindi et al., 2014. Our review indicates that both of these models give <br /> similar,and for some instances, increased ground motions for normal-faulting earthquakes which <br /> dominate the hazard at Henderson. Figures 7 and 8 illustrate PGA and 1.0 sec SA predicted by <br /> the four NGA-West2 models along with the Akkar et al. (2014) and Bindi et al. (2014)for a M <br /> 6.7 normal-faulting earthquake(As discussed in Section 5,the hazard at return period of 3,000 to <br /> 10,000 years is dominated by a M 6.7 event within 10 km). Figures 9 and 10 show the median <br /> and 84` percentile response spectra for a M 7.1 event on the Williams Fork Mountain fault, <br /> which is the controlling scenario in the DSHA(Section 5.4). Based on these comparisons,we do <br /> believe the use of the NGA-West2 models coupled with the additional epistemic uncertainty <br /> adequately predicts ground motions for earthquakes in the site region around Henderson and do <br /> not believe it is necessary to include the European models in the analyses. <br /> p7.kWR_,ffi19 <br />