As a fault becomes more severely unfavourably oriented with respect to the prevailing stress field, the magnitude of the stresses needed to promote failure exponentially increase (Fig. If the fault is assumed to have negligible cohesive strength (C), the equation changes to:įor slip to occur along a fault the stresses promoting failure (τ, P f) must overcome those resisting failure (C (if present), μ s, σ n). Where τ = shear stress, C = cohesive strength of fault, μ s = coefficient of static friction (often assumed 0.75), σ n = normal stress, P f = fluid pressure (Sibson, 1988). The shear stress resolved along a pre-existing fault is governed by the following Coulomb equation: d) Steepening of a set of conjugate shears during tectonic shortening. b) Reorientation of a strike-slip fault in a tectonic shortening regime. a) Reactivation of a normal fault in a tectonic shortening regime. Diagram showing possible methods of developing high-angle unfavourably orientated reverse faults. This occurs when formerly shallowly dipping shears become progressively steeper during shortening.įigure 3.
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