  Nonlinear evolution of a trans-Alfvenic shock wave (TASW), at which the flow
velocity passes over the Alfven velocity, is computed in a magnetohydrodynamic
approximation. The analytical theory suggests that an infinitesimal
perturbation of a TASW results in its disintegration, i.e., finite variation of
the flow, or transformation into some other unsteady configuration. In the
present paper, this result is confirmed by numerical simulations. It is shown
that the disintegration time is close to its minimum value equal to the shock
thickness divided by a relative velocity of the emerging secondary structures.
The secondary TASW that appears after the disintegration is again unstable with
respect to disintegration. When the perturbation has a cyclic nature, the TASW
undergoes oscillatory disintegration, during which it repeatedly transforms
into another TASW. This process manifests itself as a train of shock and
rarefaction waves, which consecutively emerge at one edge of the train and
merge at the other edge.
