Fault-propagation fold kinematics in mechanically anisotropic rocks: controlling factors.

This study aims to define the impact of the mechanical stratigraphy, such us thin, mechanical discontinuities, on the evolution of reverse faults and their related folds. Among different mechanical discontinuities that exist in nature, my goal is to analyze the role of thin, frictional discontinuities, by means of two methodologies, i.e. analogue and numerical modeling. Analogue models use wet clay as analogue material, and they have been designed to simulate the growth of two master faults dipping at 30° in one case and 45° in another, that are the two most common dips for reverse fault in nature. For each fault dip, one or two thin discontinuities have been inserted in the clay pack. Their results are then compared with the results obtained from fully isotropic models. The results of this first study show that reactivated discontinuities affect both the development and the propagation of new faults and the shape of the associated folds. Experimental constrains of analogue models inhibit testing different frictional properties of the discontinuities, thus inhibit simulating the variety of mechanical discontinuities that exist in nature. To overcome this limitation, in a second study, I employ boundary element method (BEM) numerical models to investigate the effect of different frictional properties of the discontinuities on the reverse faults evolution. BEM models numerically reproduce the fault configurations and sequence of faulting revealed by clay analogue models, and test different coefficient of friction along a layer-parallel interface in sequential stages of deformation. The results of this second study show that different frictional properties of the discontinuities induce variation in the distribution of the slip budget along the faults and discontinuities, affecting the time span of their interaction and modifying the propagation rate of the master fault. This study thus provides new insights for an improved understanding of fault-propagation folds mechanics in regions affected by thin discontinuities. The new findings can be used to improve the existing kinematic models of fault-related folding.