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<br />. <br /> <br />. <br /> <br />1 <br />I. <br />I <br />I' <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />, <br /> <br />. <br /> <br />.- <br />.' <br /> <br />~ <br /> <br /> <br />United States Department of the lnterior <br /> <br />(:E( lLO( ;\(::\1, SUR \'EY <br />REST():\, \11'(;1:\1.-\ 220n <br /> <br />IIl'FI(:l': IfF 111E lllHF.':!IIR <br /> <br />DES 74-32 <br /> <br />,~Ull <br /> <br />" ''J/ ~ <br /> <br />Memorandum <br /> <br />To: Commissioner of Reclamation <br /> <br />, <br /> <br />Through: pll.iilistant Secretary--Energy and Hineral$ \ -;~7" <br />\ ,I'..il ~ <br /> <br />From: Director, Geological Survey <br /> <br />Subject: Review of draft environmental statement for Fryingpan- <br />Arkansas Project, Colorado <br /> <br />We have reviewed the subject draft environmental statement as you requested <br />in a memorandum of April 17. <br /> <br />Overall, the environmental impacts related to geologic conditions in <br />the project area appear to have been thoroughly considered in the <br />draft statement. However, the description of seismicity, faulting, <br />snd potential earthquake hazards is inadequate (p. 111-63 to 65). There <br />are a number of faults in this part of Colorado that cut Pleistocene <br />sediments and the movement on these faults was too recent for them to <br />be considered inactive. With respect to faulting, the environmental <br />statement (p. 111-65) refers to two U. S. Geological Survey Professional <br />Papers, one by Scott and one by Tweto. Writing of faults that he studied, <br />Scott states: "I believe that futl.!re displacement on some of the faults <br />described could result in earthquakes large enough in magnitude to en- <br />danger property or people." He concludes his paper by stating that, <br />". . . {il though the available data are inadequate to pe1'1llit prediction <br />of time of earthquakes in east-central Colorado, the geologic information <br />and seismic record suggest that earthquakes having intensities of IV or <br />less on the modified Mercalli scale will continue as recorded by Simon <br />(1969), and a rare earthquake of intensities VI or VII is probable." <br /> <br />These remarks place a different emphasis on faulting and seismic activity <br />in the project area than is presented in the environmental statement. <br />Re-evaluation of potential impacts of earthquakes and damages that might <br />result in project component failure is suggested. <br /> <br />](1-2('3 <br />