Abstract

A seismic investigation of crustal structure of the southern Rocky Mountains in 1964 and 1965 resulted in traveltime curves that have been interpreted to indicate an average crustal thickness of 48 km in the San Juan Mountains, the Sawatch Range, and the Park Range; 52 km in the Front Range; and 37 km in the Laramie Range. The upper crust west of the Front Range includes a low-velocity zone, and the velocity in the lower crust there increases gradually to 7.1–7.3 km/sec just above the Moho. The crust in the Front Range is distinctly separated into upper and lower units. The upper-mantle velocity in the Southern Rocky Mountains is about 7.9 km/sec.

The average density and velocity of the crust are lower in the San Juan Mountains, the Sawatch Range, and the Park Range than those in the Front Range. The crust in the Colorado Plateau is thinner than that in the Southern Rocky Mountains, but the crust in the Great Plains is as thick or nearly as thick as that in the Front Range.

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