  We present experiments on slow granular flows in a modified (split-bottomed)
Couette geometry in which wide and tunable shear zones are created away from
the sidewalls. For increasing layer heights, the zones grow wider (apparently
without bound) and evolve towards the inner cylinder according to a simple,
particle-independent scaling law. After rescaling, the velocity profiles across
the zones fall onto a universal master curve given by an error function. We
study the shear zones also inside the material as function of both their local
height and the total layer height.
