The effect of tectonic overloading on strain partitioning of doubly-vergent Coulomb wedges: a 2D-3D sand-box modelling approach

The preliminary results of a sand-box experimental program are presented in this paper. The aim of the study is to analyse the effect of a pre-existing load and wedge taper angle on the development and strain partitioning of a doubly-vergent Coulomb wedge. By simulating a subduction polarity reversal, two distinct and interacting thrust systems with opposite vergence were produced, and their relationship evaluated. The presence of previously built topography strongly alters the way in which deformation is distributed inside the wedge. In particular, 2D models indicate that the axial zone inherited from the first phase of contraction diminishes the block uplift concentrated above the step-up shear (or retro-thrust) during the second phase. Therefore, a high accretion rate characterises the initial stages of deformation. In 3D, this accretion produces an anomalously wide prowedge compared to theoretical model predictions for highly oblique convergent settings. Moreover, the whole wedge is not characterised by total strike-slip partitioning on a single fault.