  We perform extensive simulations of a 2D LJ glass subjected to quasi-static
shear deformation at T=0. We analyze the distribution of non-affine
displacements in terms of contributions of plastic, irreversible events, and
elastic, reversible motions. From this, we extract information about
correlations between plastic events and about the elastic non-affine noise.
Moreover, we find that non-affine motion is essentially diffusive, with a
clearly size-dependent diffusion constant. These results, supplemented by close
inspection of the evolving patterns of the non-affine tangent displacement
field, lead us to propose a phenomenology of plasticity in such amorphous
media. It can be schematized in terms of elastic loading and irreversible flips
of small, randomly located shear transformation zones, elastically coupled via
their quadrupolar fields.
