  We report on the dynamics of a model frictional system submitted to minute
external perturbations. The system consists of a chain of sliders connected
through elastic springs that rest on an incline. By introducing cyclic
expansions and contractions of the springs we observe a reptation of the chain.
We account for the average reptation velocity theoretically. The velocity of
small systems exhibits a series of plateaus as a function of the incline angle.
Due to elastic e ects, there exists a critical amplitude below which the
reptation is expected to cease. However, rather than a full stop of the creep,
we observe in numerical simulations a transition between a continuous-creep and
an irregular-creep regime when the critical amplitude is approached. The latter
transition is reminiscent of the transition between the continuous and the
irregular compaction of granular matter submitted to periodic temperature
changes.
