The rate of horizontal shortening in an orogenic wedge is the rate at which the length of undeformed crust decreases as it is incorporated into the orogen. This rate equals the rate of convergence of the foreland lithosphere toward the central surface of the orogenic belt and the rate of subduction of foreland lithosphere beneath the central surface. The rate of propagation of an orogenic wedge is the rate at which it elongates in the direction of horizontal shortening. This rate is controlled by the rates of mass accretion to the orogenic wedge and erosion. The orogenic belt drives a flexural isostatic wave through the foreland lithosphere at a velocity equal to the rate of propagation plus the rate of subduction (or convergence or shortening). In orogenic belts where the total amount of shortening cannot be reliably estimated from balanced regional cross sections, it may be possible to determine total shortening from the distance of flexural wave migration in the foreland basin and the width of the orogenic wedge. In addition, orogenic wedges may accelerate solely in response to a reduction in taper.

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