EVOLUTION OF A FRICTIONAL WEDGE USING VELOCITY AND DEFORMATION FIELDS FROM SAND EXPERIMENTS
The talk will illustrate three points: 1) The S point concept predicts a set of limiting slip lines that bound a proside, a core, and a retroside within a generalized doubly-vergent wedge. The wedge core will be remain relatively undeformed for an advancing wedge, but will deform strongly for a retreating wedge. 2) A single wedge will typically have both critical and stable regions. Stable refers to a state where the integrated strength of the wedge is greater than the stress at the base of the wedge. Accretion and erosion favor a critical wedge, whereas sedimentation, a stable wedge. 3) Normal faulting is a common feature in the retroside of a convergent frictional wedge. There is no need for over-thickening or collapse to explain these structures.
Wedge behavior will change as thermally activated viscosity starts to dominate the interior of the wedge, but many of the concepts associated with frictional wedges are applicable to viscous wedges. There is often the notion that the wedge concept is somehow in conflict with the thin-sheet model or the channel-flow model. We will show that all of these concepts are inter-related. For example, the thin-sheet model behaves similar to a wedge with an infinitely weak basal surface. The channel flow model has a flow pattern similar to a viscous wedge with a strong gravity-driven return flow.