  We investigate the down-hill creep of a layer of granular material on a slope
caused by an oscillatory variation of the size of the particles. The material
is modeled as an athermal two dimensional polydisperse system of soft disks
under the action of gravity. The slope angle is below the critical rest angle
and therefore the system reaches an equilibrium configuration under static
external conditions. However, under a protocol in which particles slowly change
size in a quasistatic oscillatory way the system is observed to creep down in a
synchronized way with the oscillation. We measure the creep advance per cycle
as a function of the slope angle and the degree of change in particle size. In
addition, we consider a situation in which the particle size oscillation
amplitude decreases with depth, as it may be argued to occur in the case of a
granular soil in an inclined terrain. In this case creep profiles that are
maximum at the surface and smoothly vanish with depth are obtained, as it is
observed to occur in the field.
