Insights into the velocity-dependent geometry and internal strain in accretionary wedges from analogue models

Abstract

AbstractAlthough the brittle material in analogue models is characterized by a linear Navier-Coulomb behaviour and rate-independent deformation, the geometry and style of deformation in accretionary wedges is sensitive to shortening velocity. In this study we have constructed a series of analogue models with various shortening velocities in order to study the influence of shortening velocity on the geometry and kinematics of accretionary wedges. Model results illustrate how shortening velocity has an important influence on the geometry and kinematics of the resulting wedge. In general, for models having similar bulk shortening, the accretionary wedges with higher velocities of shortening are roughly steeper, higher and longer, as well as having larger critical wedge angles and height. It accommodates a number of foreland-vergent thrusts, larger fault spacing and displacement rates than those of low- to medium-velocity shortening, which indicates a weak velocity-dependence in geometry of the wedge. Moreover, models with a high velocity of shortening undergo larger amounts of volumetric strain and total layer-parallel shortening than models with low- to medium-velocity shortening. The former accommodate a greater development of back thrusts and asymmetric structures; a backwards-to-forwards style of wedge growth therefore occurs in the frontal zone under high-velocity shortening.