REP33384

• Permit No: M1977342
• IBM Index Class Name: Report
• Doc Name: PROBABILISTIC SEISMIC HAZARD ANALYSIS OF HENDERSON TAILING DAM NORTH CENTRAL COLO
• Media Type: D
• Archive: No

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However, as will be discussed, the Golden fault is too distant and has too low of a slip rate
to contribute significantly to the seismic hazard at the damsite.
Mosquito and T.eadville Faults
The Mosquito fault is anortheast-striking, steeply northwest-dipping normal fault that borders
the western flank of the Mosquito Range (Plate 1). This fault has a totad length of
approximately 62 km (Kirkham and Rogers, 1981). The total length appazentl;y includes a
N40°E fault southeast of Leadville (J. Unruh, William Lettis & Associates, personal
communication, 1995) which we have not included. We estimate a total fault length of 53
km. The lengths of the northern and southern segments of the Mosquito fault are estimated
to be 28 km and 25 km, respectively.
We have considered the faults azound Leadville as a sepazate seismic source as they appear
to be a transfer zone between the east-dipping Sawatch fault to the south and the west-
dipping Mosquito fault to the north. The Leadville faults include several strands which span
a distance of approximately 19 km from northeast to southwest.
The mapped trace of the Mosquito fault as portrayed by Kirkham and Rogers (1981) differs
from the system of faults along the western mazgin of the Ten Mile Range anal Mosquito
Range as mapped by Tweto et al. (1978). The mapped trace shown on Plate 1 follows those
mapped by Tweto et al. (1978). Near Leadville, the Mosquito and Leadville faults have a
total vertical displacement of about 3660 m, and neaz the town of Climax, the displacement
could be as great as 4720 m (Kirkham and Rogers, 1981). Evidence for Quaternary
movement along this fault is relatively scarce. Scarps and anomalous features in moraines
and colluvial deposits just south of Climax may reflect recent fault movement (1?:irkham and
Rogers, 1981), although this is uncertain. The leadville faults deform late Neogene strata
(Tweto et al., 1978).
Since no slip rate data are available for the Mosquito fault and the Leadville faults, a slip rate
of 0.1 mm/yr was assumed based on slip rate estimates for the Sawatch fault, which is the
southern continuation of the northern Rio Grande rift. Mean maximum mal;nitudes aze
estimated to be MW 6.7 for both segments of the Mosquito fault and M„ 7.0 for rupture of
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