Controls of permeability on the mechanical evolution of shortening basins

We follow the evolution of faulting in an idealized prismatic basin during lateral shortening as a result of poromechanical interactions. This includes the deformation-induced generation (compaction) and dissipation (hydraulic fracturing) of pore fluid pressures and the resulting natural evolution an underlying decollement and fault structures. Modeling is capable of representing the form of fault structures that may develop within a basin as a result of shortening. Thrust faulting develops as overpressures evolve to trigger failure. A decollement forms within the system at the boundary with the substrate where overpressures drive failure in extension, by hydrofracturing. Failure in the basin overlaying the decollement initiates from these overpressures at the decollement. Where the evolution of permeability with shear strain is artificially suppressed, pervasive shear develops throughout the basin depth as fluid pressures are pegged everywhere to the lithostat. Conversely, where permeability is allowed to increase with shear strain/rupture, faulting first nucleates at the decollement and localizes upwards through the section. Correspondingly, permeability evolution with shear is an important, likely crucial, feedback in promoting localization, as failure is concentrated at the limits of the upward-migrating fault-tip. Elevated pore pressures approaching the lithostat are localized at the hanging wall boundary of the faults. As faults extend, horsts and graben are ultimately isolated, and evolve with distinctive surface topography and separate pore pressure signatures. Horsts have elevated fluid pressures and reduced effective stresses at their core, and graben the converse.