Abstract

Scaled experimental models show that the presence of a viscous layer, such as salt, facilitates the development of extensional forced folds above active normal faults. The geometries of the extensional forced folds and their associated secondary fault patterns depend on the thickness and viscosity of the viscous layer, the thickness of the cover sequence, the strength and ductility of the cover sequence, and the magnitude and rate of displacement on the underlying master normal fault. Increasing the thickness of the viscous layer and the cohesive strength and ductility of the overburden enhances the decoupling between the deep and shallow deformation. Alternatively, increasing the viscosity of the viscous layer, the thickness of the overburden, and the magnitude and rate of displacement on the master normal fault reduces the decoupling between the deep and shallow deformation. Enhanced decoupling facilitates the formation of broad extensional forced folds and the development of detached secondary faults both near and far from the master normal faults. The model-predicted deformation patterns closely resemble those observed in the Gulf of Suez, the Haltenbanken area of offshore Norway, and the Jeanne d'Arc Basin of the Grand Banks, offshore southeastern Canada.

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