C153629 Feasibility Study - Laserfiche WebLink

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I I I I I I I I I I I I I I I I I I I CHAPTER 2 REGIONAL SEISMICITY EVALUATION Previous evaluations of damsites on Muddy Creek just upstream of Kremmling indicated the potential presence of active faults in the region. Strong evidence of potentially active faults near the damsites would require selection of higher than normal earthquake loading fac- tors to be employed in the dam design and would make construction cost estimates higher. The damsites on Rock Creek and Muddy Creek are only 12 miles apart and both could be affected by seismic activity in the region. Of particular concern is the Antelope Pass Fault which is located north and east of Kremmling extending in a near true north direction. This fault has been classified as a potentially active fault by the Colorado Geological Survey and large seismic design loads have been considered necessary in some of the previous Muddy Creek Dam design evaluations. Due to the uncertainty of the seismic risk in the region, a Seismotectonic Hazard Evaluation was performed as a part of this feasibility study to provide guidance in preparing the preliminary dam designs. Michael W. West and Associates was selected to conduct a Phase I and Phase II seismotectonic hazard evaluation for the proposed damsites on Rock Creek and Muddy Creek. The Michael W. West and Associates' evaluation is included as Appendix D of this report and summarized below. Field examinations of the regional geology and faulting patterns were made in October of 1985. The observations were assisted by the use of available regional geologic mapping and high altitude color infrared areal photographs. The evaluation objectives were to: o Compile and evaluate instrumentally-recorded seismicity and historic fault reports in the region surrounding the proposed damsites. o Evaluate the potential for seismogenic surface faulting in and near the project area. 2 - 1 7042W/5020W