Growth of fractal fault patterns

Experiments on the formation of faults in a laboratory model of the Earth's crust are presented; they respect its vertical rheological stratification, a brittle layer on top of ductile layers. As a result of the competition between the different nature of the brittle and ductile-layer deformations, complex fractal patterns of faults are formed with fractal dimension 1.70±{}0.05 independent of the fault densities associated with different brittle-ductile coupling. We propose a kinematic formulation of the mechanical problem which suggests an analogy with previously studied fractal-growth problems.