Classic crustal strength-depth plots assuming constant over pressured  λ are generally quite misleading because constant λ > λ_hydrostatic is not a reasonable assumption, 

certainly in deforming sedimentary basins.  Typically, fluid pressures are hydrostatic until the fluid-retention depth is reached, below which fluid pressure increases along the lithostatic gradient because the increases in overburden are supported by the fluid rather than the rock.  An exception to this is permeable overpressured sands embedded in over pressured shales.

The general result is that effective stress and both rock and fault strength become regionally constant with depth, as shown in the attached figures, including an example from offshore Texas for which in-situ stress measurements are available.

On Jun 4, 2018, at 8:32 AM, Ben van der Pluijm <[log in to unmask]> wrote:

FIGURE 3.26. Graph showing variation in differential stress necessary to initiate sliding on reverse, strike-slip, and normal faults, as a function of depth. The relationship is given by Equation 8.1, assuming a friction coefficient, μ=0.75, and a fluid pressure parameter, λ=0 (no fluid present) and λ = 0.9 (fluid pressure is 90% of lithostatic pressure).
From PSG&T

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