Modelling of structural complexity in sedimentary basins: The role of pre-existing faults in thrust tectonics

Abstract Analogue and numerical models have been used to study the role of pre-existing faults in compressive regimes. From a theoretical point of view, reactivation is mainly controlled by fault attitude, stress regime and frictional properties of fault planes. In scaled-down sandbox experiments, precut faults are introduced in the homogeneous granular media with a nylon wire which is forced through the sand cake producing a thin planar disturbed zone. Systematic experiments of thrust inversion with various dips and strikes of such planar discontinuities have been modelled. Comparison of experimental results with theoretical diagrams indicate that disturbed zones have a friction angle which is 10–20% lower than the homogeneous sand and that the compressive regime in the sandbox has a shape factor close to 0.4. The static analysis of fault reactivation is in accordance with the experimental observations except for pre-existing faults dipping at very low angle. However, numerical modelling using the Udec code shows that low-angle faults can be reactivated as a result of stress concentration in the lower part of the fault. In addition, sandbox experiments indicate that in thrust systems, reactivation of pre-existing faults is not only dependent on their attitude but also on their spacing and location relative to the thrust system.