Critical taper

Every wedge has a certain "critical angle", which depends on its material properties and the forces at work.

[1][2] This angle is determined by the ease by which internal deformation versus slip along the basal fault (décollement) occurs.

If the wedge deforms more easily internally than along the décollement, material will pile up and the wedge will reach a steeper critical taper until such a point as the high angle of the taper makes internal deformation more difficult than sliding along the base.

If the basal décollement deforms more easily than the material does internally, the opposite will occur.

The critical taper concept can thus explain and predict phases and styles of tectonics in wedges.

An important presumption is that the internal deformation of the wedge takes place by frictional sliding or brittle fracturing and is therefore independent of temperature.

[3] The critical taper concept assumes mechanical equilibrium, which means the compressional force (the tectonic push) that created the wedge will be equal to the resisting forces inside the wedge.

These forces resisting the tectonic force are the load (weight) of the wedge itself, the eventual load of an overlying column of water and the frictional resistance at the base of the wedge (this is the shear strength at/of the base,

) times the gravitational acceleration (g), working on a surface with dimensions dx and dy (unit vectors).

) is the resisting force of the load of an eventual water column on top of the wedge.

This can be written as: The pushing force is here assumed to be working on the total height of the wedge.