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<br /> <br /> G <br />d <br />ifr <br />Th <br />thi <br />i <br />i <br />t <br />f <br />h <br />l <br />i <br />b <br />bl <br />d <br />h <br />h h <br />fl <br /> ran <br />e r <br />. <br />e <br />nner se <br />smogen <br />c crus <br />o <br />t <br />e <br />atter <br />s pro <br />a <br />y <br />ue to <br />ig <br />ow <br />eat <br /> (Wong and Chapman, 1990). <br /> <br /> Vertical separation rates estimated from published and unpublished data were ~~onverted to <br /> average slip rates, assuming a fault dip of 60°. We determined a range in slip rites for each <br /> fault based on a slip rate distribution developed for Basin and Range and Rio Grande rift <br /> faults using both long-term and short-term slip rate data (Wong et al., 1995). 'Che mean of <br /> the slip rate distribution was scaled to the average slip rates estimated for the 1.'aults in this <br /> study and the 10th, 50th and 90th percentile values extracted and weighted 0.3, 0.4 and 0.3 <br />ti <br />l <br />Th <br />i <br />ht <br />d <br />f th <br />th <br />l <br />i <br />i <br />l <br />th <br />li <br />t <br /> respec <br />ve <br />y. <br />e we <br />g <br />e <br />mean o <br />ree va <br />e average s <br />ese <br />ues <br />s approx <br />mate <br />y <br />p ra <br />e <br /> (Table 1). <br />' <br /> Maximum magnitudes were estimated using empirical relationships derived b.y Wells and <br /> Coppersmith (1994) based on surface rupture length and fault rupture area for normal <br /> faulting. Rupture areas were calculated from potential rupture lengths, a fault di.p of 60° and <br />' a seismogenic depth of 15 km. Faults less than about 20 km long were assigned a maximum <br /> magnitude of MW 6.5, the threshold for surface faulting in the Basin and Range province <br /> (dePolo, 1994). <br /> Chase Gulch Fault <br /> <br /> The Chase Gulch fault is anorthwest-striking fault located just west of Colorado Springs <br /> (Plate 1). This fault lies along the northeast margin of Spinney Mountain, a Lazamide-age <br /> uplifr formed by anticlinal folding above the Elkhorn thrust fault (Unruh et al., 1995b). The <br />' Chase Gulch fault is approximately 29 km long and dips to the northeast. Tlus fault has <br /> approximately 2.5 m of post-Pinedale displacement, which implies a vertical sel~azation rate <br /> of 0.07 to 0.2 mm/yr, with a preferred rate of 0.14 mm/yr during the late Quaternary (Shaffer <br /> and Williamson, 1986). We estimate a preferred slip rate of 0.16 mm/yr. The mean <br /> maximum magnitude is Mw 6.7 (Table 1). The Chase Gulch fault is considered ro be active. <br /> <br /> <br />1 <br />H1CONIRACT234561DUP9 9 M0309951609 <br />