  Scaling properties of patterns formed by large contact forces are studied as
a function of the applied shear stress, in two-dimensional static packings
generated from the force network ensemble. An anisotropic finite-size-scaling
analysis shows that the applied shear does not affect the universal scaling
properties of these patterns, but simply induces different length scales in the
principal directions of the macroscopic stress tensor. The ratio of these
length scales quantifies the anisotropy of the force networks, and is found not
to depend on the details of the underlying contact network, in contrast with
other properties such as the yield stress.
