Figure 4.
Physical model showing transition from (A) normal faulting to (B) separated polygons under multidirectional extension triggered by gravity. The model comprises a brittle layer of dry blue sand overlying a viscous layer of transparent, colorless silicone polymer (polydimethyl-siloxane). Initial fault patterns are controlled by the surface dip of the model and the lateral boundaries of the mobile unit (A). Thickness variations within the mobile unit result in multidirectional extension due to enhanced flow within the thicker mobile unit, separating and rotating the polygons (B). F1 and F2—faults; x and o—arbitrary marker points.