Cross plots between the λ and effective coefficient of basal friction. (A) Calculated critical values of the Hubbert-Rubey pore fluid pressure ratio (λ) and basal friction of the wedge. Extensionally critical states form on the left limb of the critical-state curve, whereas compressively critical states form on the right limb. The white area below the curve represents the stable region. The straight-line tangent to critical-state curve represents the condition of , where α is the surface slope angle and β is the décollement dip angle. (B) Parameter sensitivity of the taper angle; data were modified and applied to survey sites AM101 and SR101 (from Wang et al. ). Calculations were performed assuming ρ = 2,700 kg/m3, ρw = 1,000 kg/m3.