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Abstract

This thesis addresses the complexity in the patterns of deformation in accretionary wedges based on analogue modelling. A combined approach of 1) statistically assessing results from sand wedges 2) mechanically analyzing fault behavior in the structural evolution of sand wedge and 3) comparing varying wedge geometry and dynamics to theory, are used in an effort to unravel the complexity that develops as the wedge evolves. This thesis comprises of three manuscripts addressing these three approaches respectively. The experimental database is derived from analysis of 27 analogue sand wedge models where the friction of the basal décollement is varied. The kinematics of the analogue sand wedge is monitored using Particle Image Velocimetry (PIV) that provides detailed information on the displacements in the wedge. The statistical approach (Chi square test, ANOVA test) consists of quantifying the degree of both intrinsic variations in the results of the model and extrinsic variation caused by the varying basal friction. In particular the statistical study shows that intrinsic variability of fault and wedge observables is related to the mechanics and material properties of the wedge. In addition, results show that analogue experiments are reproducible. The next study presented in this thesis reflects on the faults of the wedge. Fault activity, in particular fault formation, reactivation and underthrusting are described. The observations are explained mechanically in relation to the fault geometry and the changing frictional properties along the fault plane. It is also demonstrated that fault activity governs the shape, activity and eventual zonation of the wedge. Additionally, a comparison between two theories 1) Critical taper theory and the 2) Minimum work theory is performed to recognize which theory best represents the deformation in accretionary wedges. The critical taper theory focuses on the geometry of the wedge and the minimum work theory focuses on the energy in the wedge. It is evident that both theories are applicable, however at different stages of an accretionary cycle. Overall, the minimum work theory determines the path of deformation needed to reach that geometry determined by the critical taper theory. Research to explore the role of ductile behavior in the wedge is also initiated. Preliminary stages of the research include the characterization of a new elasto-plastic viscous material called Carbopol that behaves in a viscous manner after a certain yield strength is overcome i.e. Herschel Bulkley fluid. A rheological study tests the effect of concentration of three different types of commercial Carbopol products. Besides this research, the monitoring of forces in analogue models is also attempted with a new setup. The combination of high resolution force recordings and visual PIV data provides an insightful view into the dynamics of the model.