A review of heterogeneous materials and their implications for relationships between kinematics and dynamics in continents

The variation of mechanical properties as a function of depth in the lithosphere controls the relationship between surface deformation and whole-lithosphere deformation. Where mechanical competence (elastic strength or viscous stiffness) is a continuous function with depth, surface deformation can be used to constrain either force balance or rheological parameters for the lithosphere. However, where competence is vertically discontinuous, the surface deformation and deformation at depth may have a range of relationships, including complete independence. Therefore, both inversions and forward models designed to test either rheology or stress state are highly sensitive to the a priori choice of a mechanical model.