Constant-thickness deformation above curved normal faults

Extensional fault systems are commonly described using models that assume l ayer-oblique heterogeneous simple shear deformation in fault blocks. These models are colloquially known as vertical or inclined shear models. Less co mmonly, layer-parallel heterogeneous simple shear is employed; these models are called constant-thickness/flexural-slip models, and have the geometric property that they conserve both bed length and bed thickness. Although po pular, vertical or inclined shear models suffer from the limitation that th ey do not explain two widely observed features of extensional fault systems : crestal collapse grabens, and downwardly blind faults within the hanging wall. Currently used constant-thickness/flexural-slip models are severely l imited by their inability to 'forward-model' faults with dips (angular bend s) greater than 30 degrees. We have modified the most widely used constant- thickness/flexural-slip model so that it can be applied to faults with dips or angular bends greater than 30 degrees. The resulting model can be used to describe the constant-thickness geometry of hanging walls developed abov e normal faults of any shape. Alternatively, the model can be used to predi ct the amount and location of departures from constant-thickness (and const ant bed length) deformation in a fault hanging wall, manifest at large-scal e by crestal collapse grabens and downwardly blind faults, or at small-scal e by sub-seismic-resolution faulting. (C) 1998 Elsevier Science Ltd. All ri ghts reserved.