To what degree the geometry and kinematics of accretionary wedges in analogue experiments is dependent on material properties

Abstract. Cohesion and friction coefficients are fundamental parameters of granular materials used in analogue experiments. Thus, to test the physical characteristics and mechanical behaviour of the materials used in the experiments will help to better understand into what degree the results of experiments of geological processes depend on the material properties. Our test suggests significant differences between quartz sand and glass bead, in particular the shape factors (~ 1.55 of quartz sand to ~ 1.35 glass bead, angular to rounded) and grain sorting (moderately to well sorted). The glass beads show much better grain sorting and smaller shape factors than the quartz sand. Also they have smaller friction coefficient (~ 0.5 to ~ 0.6) and cohesion (20–30 Ma to 70–100 Ma), no matter of the grain size in our tested samples. The quartz sand shows much smaller friction coefficient (~ 0.6 to ~ 0.65), and smaller cohesion (~ 70 Pa to ~ 100 Pa) than that of smaller grain size sand. We have conducted four sets of analogue experiments with three repeats at the minimum. Our models show that material properties have important influence on the geometry and kinematics of the accretionary wedge. Although the difference in geometries are small, models with larger grain size develop wedges with higher wedge height, larger taper, shorter wedge length and less number of faults under the same amount of bulk shortening. In particular, models with basal detachment (even with 1 mm thickness), show significant difference in geometry and kinematics with that of quartz sand. We thus argue that the geometry and kinematics of the wedge appear to be significantly influenced by relative brittle and ductile strengths, and, to a lesser degree by the layering anisotropy. The basal detachment (even of tiny thickness) determines the first-order control on the location and development of accretionary wedge, in a contrast to the physical properties of brittle materials.