Fault Development In The Imbricate Thrust Pile Under Variable Basal Friction And Slope Geometry From The Sand Box Analog Modeling

We performed a series of sand box experiments to model mechanical constraints, especially variable geometries and friction of the decollement, on the fault development at the leading edge of imbricate thrust piles in natural accretionary wedges. The models with different basal friction (low and high) and slope geometry (0 and 5 degrees) are conducted by using Toyoura sand with grain size less than 0.18 mm and model dimension of 12.5 cm in length by 10 cm in width by 0.6 cm in thichness. All the models are shortened under constant slow rate from the rear wall side and the other side is fixed. The results from the selected four models show that the growth of sand wedge depends on the basal slope geometry. When the basal slope is horizontal, the wedge grows up continuously, and in contrast to this, the wedge grows up episodically when the basal slope is dipped five degrees to hinterland. Total of six faults developed after 48 percent bulk shortening in low basal friction models whereas after 57 percent in high basal friction models. Four faults formed in linear space before 20 percent bulk shortening in all models. After 20 percent bulk shortening, fault spacing become twice of before. Otherwise, after 20 percent of bulk shortening the wedge grew up more or less equilibrium and fault development was controlled by the basal shear stress and friction in order to attain critical wedge growth. Key words: Analog modeling, sand box, fault development, basal friction, slope geometry, accretionary wedge, decollement