  Refraction and deflection of shear zones in layered granular materials was
studied experimentally and numerically. We show, that (i) according to a recent
theoretical prediction [T. Unger, Phys. Rev. Lett. 98, 018301 (2007)] shear
zones refract in layered systems in analogy with light refraction, (ii) zone
refraction obeys Snell's law known from geometric optics and (iii) under
natural pressure conditions (i.e. in the presence of gravity) the zone can also
be deflected by the interface so that the deformation of the high friction
material is avoided.
