Fig. 3
From: Preparation zones for large crustal earthquakes consequent on fault-valve action
Adapted from Fig. 2 in Sibson (2020)
Plot of the pore-fluid factor, λv = Pf / σv, required for hydraulic extension fracturing versus depth for the three basic stress regimes with σv = σ1 (normal fault regime), σv = σ2 (strike–slip fault regime with σv = 0.5 (σ1 + σ3)), and σv = σ3 (thrust fault regime) following the methodology of Secor (1965). Maximum differential stress limited by tensile strengths, To = 5 MPa (average sedimentary rock) and 10 MPa (competent sedimentary rock) (Lockner 1995).