Quantification and visualization of finite strain in 3D viscous numerical models of folding and overthrusting

Abstract

Finite strain analysis and three-dimensional (3D) numerical modeling are important methods to understand the deformation history of rocks. Here, we analyze finite strain in 3D numerical simulations of power-law viscous folding and overthrusting. Simulations with different and laterally varying detachment geometries cause a lateral transition from folding (for thicker detachments) to overthrusting. We compute the 3D finite strain tensor, the principal strain values and their orientations. We compute the Nádai strain, εS, and the Lode’s ratio, ν, representing the strain symmetry (constriction or flattening). We apply Hsu diagrams to visualize strain distribution in εS - ν space, in combination with color-coding, indicating the corresponding position of strain data in the 3D model. We analyze the orientation and spatial variation of finite strain with polar and rose diagrams and quantify the spatial and temporal evolution of finite strain with strain profiles. Our results show that: (i) the magnitude of εS generally increases from folding to overthrusting, (ii) an initial flat ramp geometry of the detachment generates a distinctive pattern of εS, (iii) lateral variations of εS and ν can be used to identify lateral variations in sub-surface structures, and (v) internal strike-slip shearing is generated due to the folding–overthrusting transition.