We estimate strain rates of three parameters that describe the buildup of a tectonic wedge (Jura front, France). The uplift rate on frontal ramps decreases with the slip on the ramps and the coeval increase of vertical loads. The migration rate of the tip of the sole thrust appears to be episodic and faster than the translation rate of the backstop. The long-term tilting rate appears to be constant, whereas the short-term rate is slightly slower. We propose a model of wedge growth that proceeds without underthrusting. In a prefractured medium, the wedge would activate the frontal ramp with a weaker frictional resistance than the forward décollement. An instantaneous forward jump of the deformation front would occur when the resistance on the ramp equals the resistance of the frontal décollement. This model differs from those proposed for accretionary zones, and relates to the backstop of a single tapered orogenic belt.