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SECT NONE Imroduction <br /> At the request of Freeport-McMoRan, Inc. (FMI), updated site-specific seismic hazard analyses <br /> of the Henderson Mill tailings dams have been performed incorporating new information on <br /> seismic sources, recent data on foundation shear-wave velocities (Vs) and updated ground <br /> motion prediction models. Additionally,time histories consistent with the 500 and 10,000-year <br /> return period Uniform Hazard Spectra(UHS)were developed for use in dynamic analyses of the <br /> tailings dams. <br /> As part of this update,a review of current literature and recent research on seismic sources which <br /> may contribute to the hazard at the site was performed. This desktop study incorporates new <br /> data from the U.S. Bureau of Reclamation (USBR) on studies of the Frontal fault along with <br /> some results from ongoing mapping in the region (McCalpin et al., 2012a; 2012b), including <br /> mapping that uses recently flown LIDAR (laser imaging detection and ranging system) data of <br /> the upper Arkansas Valley and nearby areas (e.g., Bohanon and Ruleman, 2013; Shroba et al., <br /> 2014),which covers parts of the southern Mosquito fault and other nearby Quaternary faults. <br /> Since the previous seismic hazard analyses of the Henderson Mill tailings dam, an update to the <br /> Next Generation of Attenuation (NGA) ground motion models has been released. This study <br /> incorporates the NGA-West2 ground motion models, which were developed based on an <br /> expanded strong motion database and published by the Pacific Earthquake Engineering Research <br /> (PEER)Center in 2013 and 2014. <br /> The Henderson Mine is located in the Southern Rocky Mountains of central Colorado, which is <br /> characterized by a low to moderate level of historical seismicity(Figure 1). Although the largest <br /> historical earthquake is only a moment magnitude (M)6.6 in 1882,the mine is located adjacent <br /> to Quaternary active faults that have the potential to generate earthquakes as large as M 7 or <br /> larger(Figures 2 and 3). <br /> A primary objective of this study is to estimate the levels of ground motions that could be <br /> exceeded at specified annual frequencies(or return periods)at the sites of Tailings Dams 1 and 3 <br /> by performing a probabilistic seismic hazard analysis (DSHA). A traditional deterministic <br /> seismic hazard analysis (DSHA) was also performed for comparison purposes. Based on the <br /> results of the PSHA and DSHA, the mean 10,000-year return period Uniform Hazard Spectrum <br /> (UHS) was selected for use in stability analyses and time histories were developed consistent <br /> with this spectrum. For use in operating level stability analyses, time histories were also <br /> developed consistent with the 500-year return period UHS. <br /> 1 <br />