Application of geometric models to inverted listric fault systems in sandbox experiments. Paper 2: insights for possible along strike migration of material during 3D hanging wall deformation

Fault geometry is a primary control on hanging wall deformation. In this study, a series of positive inversion analogue experiments was conducted using rigid fault surfaces of true 3D geometry, with consistent listric geometry along the transport direction. The deformed geometry of the top horizon of the syn-extension sequence on vertical serial sections was examined with a conventional 2D geometric restoration technique to calculate the inclined antithetic shear angle that best approximates the actual fault shape, and to estimate the amount of apparent horizontal shortening during contraction. The apparent shear inclination and the estimated apparent shortening show a systematic change along strike, corresponding to the plan geometry of the master detachment surface. At the hanging wall above embayments in the fault geometry, the uplift is highest, the apparent shear inclination is gentlest and the apparent horizontal shortening is greatest. In contrast, the apparent shear inclination is steepest and the estimated shortening is smallest above salients in the master detachment geometry, where the uplift is lowest. These changes suggest that the hanging wall displacement had an along-strike component during deformation; the hanging wall material moves from the regions above salients to those above embayments in the detachment surface during contraction. Average of the estimated apparent shortening was smaller than the actual amount of the experiments, probably due to tectonic compaction. This study shows that the geometry of the master detachment in plan view has the primary control on the lateral variation of the hanging wall deformation. The data presented in this paper help understand 3D geometric relations between the hanging wall deformation and the underlying detachment surfaces.