Understanding the evolution of faults from their blind phase to a mature stage (i.e. surfacebreaking faults) is fundamental in active tectonic studies because conventional analyses for identifying and characterizing the earthquake potential of large continental faults rely largely on surface evidence of faults. In brittle crust, faults form and propagate by linking small tensile cracks. A plethora of studies dealt with fault propagation mechanisms using different approaches, from theoretical formulations to field analyses to numerical and analogue simulations (see Mandl, 2000; Scholz, 2000; and Gudmundsson, 2011 for a summary). In an isotropic material, the propagation of faults is controlled by rock toughness and applied stress. In nature, rocks exhibit intrinsic mechanical anisotropies that affect stress trajectories and consequently the nucleation and growth of faults. Examples of mechanical heterogeneities in nature arelithologicalchanges, layering, fluids, inherited faults etc. Herewefocusontherolethatpre-existingthin mechanical discontinuities with different orientations may play in the propagation of an extensional fault. We present a series of clay (wet kaolin) analog models simulating the evolution of a buried extensional structure. To analyze how mechanical discontinuities affect strain distribution and new extensional faults formation,
we introduce in the models frictional weaknesses with different orientatio
