  Shear zone formation is investigated in slow 3D shear flows. We simulate the
linear version of the split-bottom shear cell. It is shown that the same type
of wide shear zones is achieved in the presence as well as in the absence of
gravity. We investigate the relaxation of the material towards a stationary
flow and analyze the stress and the velocity fields. We provide the functional
form of the widening of the shear zone inside the bulk. We discuss the growth
of the region where the material is in critical state. It is found that the
growth of the critical zone is responsible for the initial transient of the
shear zone.
