Deformation and stability of over‐pressured wedges: Insight from sandbox models

Abstract

In the well‐known and widely used critical taper model of accretionary wedges, pore pressure is introduced as a first‐order parameter. Despite the fact that the importance of the pore pressure on deformation is largely accepted, the theoretical predictions of the critical model has never been experimentally confirmed for over‐pressured wedges. To fill this gap and to understand how pore pressure may influence deformation within a wedge, we performed scaled experiments under conditions close to the critical taper hypothesis. The wedges were built with a non‐cohesive sand and lied on glass microbeads layer to insure a weak décollement. As we applied horizontally varying fluid pressure at the base of the model, the pore pressure ratioλ was almost constant in the whole wedge. Combining these experiments with an optical image correlation technique (Particle Imaging Velocimetry), we followed the strain in the model during the shortening. We highlighted three different modes of deformation which are strongly influenced by the pressure ratio, λ, and the wedge taper. Although we found a pretty good agreement between the experimental observations and the critical taper model predictions, it appears that the transition between sub‐critical and super‐critical conditions is not sharp as described by the critical taper model but continuous. The distance to the critical taper condition, which depends on both the topographic angle,α and the pressure ratio, λ seems to control the propagation rate of the décollement and the strain localization within the wedge.