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<br />occurring 7600+120 ybp. USBR (1980, 1990) assigned and MCE of <br />M,,=7.3 at a focal depth of 7 to 10 km to the Sangre de Cristo fault. <br />We include the Sangre de Cristo fault in the PSHA at a maximum <br />magnitude of 7.25 and average recurrence of 2500 years. <br />Faults near Spinney Mouutain, South Park <br />Studies in conducted for Spinney Mountain Dam (Converse, Wazd, <br />Davis, Dixon, 1980) 31 miles (52 km) east of the Trout Creek dam <br />site, found strong evidence of late Pleistocene (13-30 thousand yeazs <br />before present) faulting and proposed a local MCE of Richter magni- <br />tude M~=6.2. <br />We include the Chase Gulch fault at a maximum magnitude of 6.2 and <br />average recurrence of 13,000 yeazs. <br />Rocky Mountain Arsenal <br />The Rocky Mountain Arsenal source zone specifically includes earth- <br />quake activity within the western Denver Basin triggered by borehole <br />injection of waste fluids at the Rocky Mountain Arsenal (RMA) begin- <br />ning in March 1962. The RMA source zone is defined by epicenters of <br />the 1967-8 and 1981 earthquake swarms. The 1967-8 earthquakes aze <br />chazacterized by normal faulting along a fault plane striking N50°W <br />with most of the events occurring at depths of between 3 and 8 km. <br />The Composite focal mechanism for the earthquake sequence of Mazch <br />to April 1981 shows a combination of reverse and strike-slip faulting <br />with nodal planes of N58°W, 60°NW and N7b°W, 40°SW (Bollinger <br />and others, 1983). <br />Kirkham and Rogers (1981) stated that they found no geophysical or <br />geological evidence for disruption of late Tertiary strata related to <br />faulting. Possible evidence for Quaternary fault displacement consists <br />of a 20-foot step in the Broadway terrace (Pre-Wisconsin age) north- <br />west of the RMA disposal well within the elliptical zone of earthquake <br />epicenters (DeVoto, 1968). Kirkham and Rogers, however, concluded <br />that the existence of the "Derby fault" was uncertain. <br />28 <br />