In this paper sandbox modelling was used to investigate the dynamic effect of localised syntectonic erosion and\or sedimentation on the deformation mechanics of accretionary systems. High obliquity was chosen as the main boundary condition to analyse 3D strain partitioning of a doubly-vergent Coulomb wedge for the particular case in which a subduction po1artv reversal event affected wedge development. In the experiments the first phase of shortening ( P1) produces a preexisting topography affecting wedge development during second phase ( P2). The elevation potential can be varied in the models via sequential events of syntectonic denudation and/or sedimentation performed on distinct sectors of the deforming wedge. Experimental results suggest that the parallelism between the imbricates at the thrust front and the strike-slip fault at the rear of the prism predicted by theoretical models is valid only at steady-state when failure conditions exist everywhere at the basal deĢcollement. Before this stage different velocity fields characterise mass transfer in distinct sectors leading to unexpected wedge behavior during which superficial extension or compression, both located i n the axial zone, predate the full development of a strike-slip fault.
