Figure 23

Maximum apparent viscosity in the convective cell at the point of lithospheric failure as a function of the viscosity contrast in the absence of yield stress. Black, exponential viscosity with constant τ _{y,c r} ; red, Arrhenius viscosity with constant τ _{y,c r} ; green, exponential viscosity with constant τ y,c r′; blue, Arrhenius viscosity with constant τ y,c r′.