Effect of Friction and Strength Properties of the Medium on Shear Band Formation in Thrust Structures

Resumo

Thrust faulting has been studied within the framework of a tectonic wedge model. A variant of the model was proposed which accounts for changing friction between the wedge bottom and a rigid foundation during irreversible deformation. Some specific deformation structures typical for thrust zones were revealed; their formation conditions were estimated. The range of friction coefficient values was determined in which the friction coefficient has a general effect on thrust structures. The nucleation sites and the main patterns of fault structures were described depending on the parameters of the medium and friction conditions at the bottom. The shear bands can initiate both from the layer bottom and from the surface, at irregularities of the relief, as well as at the front of the plastic deformation zone. It was found that listric faults initiate at the layer bottom in a medium with low shear strength. In a high strength medium, shear banding starts from the wedge surface. The calculations showed that the main factors determining the overall pattern of the deformation structure and fault structure in the thrust zone are the strength characteristics of the medium and friction between the deformed layer and the rigid foundation. The deformation processes were modeled by solving a system of dynamic equations of an elastoplastic medium using an explicit numerical scheme under plane strain. The behavior of the medium was described by a model with the Drucker—Prager yield surface and non-associated flow rule, with account for hardening and softening of the medium during plastic deformation.