Analogue modelling of fault reactivation: tectonic inversion and oblique remobilisation of grabens

Abstract

Analogue models of sand above a silicone layer were examined to determine the effects of normal fault reactivation. Models were first subjected to extension, which lead to the formation of two linear grabens. Each model was then subjected to a second phase deformation, either parallel or oblique to the previous initial extension, and either extensional or contractional. The influence of sedimentation has been evaluated using experiments with and without sedimentation. In cases of oblique secondary deformation, all newly formed faults were parallel to the older grabens, thus they were oblique to the direction of the principal stress directions during the second deformation phase. In experiments without sedimentation, all older faults were reactivated, whereas in experiments with sedimentation, some of the older faults were not reactivated. In the case of an oblique compressional secondary deformation phase with post rift sedimentation, strain partitioning occurred between reactivated older normal faults and new reverse faults. σ2 was vertical on reactivated normal fault planes, whereas σ3 was vertical on reverse fault planes. In the case of oblique compressional secondary deformation phase without post rift sedimentation, no strain partitioning was observed. In this model, σ3 was vertical on every fault plane. It is therefore concluded that sedimentation within grabens induces a variation of stress orientation and strain partitioning.