  The propagation of shear Alfven wave packets in inhomogeneous magnetic
fields, at the origin of their distortion, regardless of the occurrence of
non-linear coupling, is considered. It is shown that the distortion mechanism
can be regarded as mixing process and hence, standard "phase mixing"
corresponds to the effect of an "Alfvenic" shear flow while enhanced
dissipation at a magnetic X-point corresponds to mixing by an "Alfvenic" strain
flow. The evolution of the global wave field is supposed to result from the
dynamics of a superposition of wave packets and a kinetic equation for the wave
energy is obtained following this eikonal (WKB) description. Since shear Alfven
wave packets experience continuous shearing/straining while transported by an
inhomogeneous Alfvenic flow $\mathbf{V}_{A}$, their mixing process, in physical
space, is also a cascade of wave energy in k-space. The wave energy spectrum
resulting from this linear mechanism of energy transfer is determined for the
special case of waves propagating along chaotic magnetic field lines, the
analog of a chaotic mixing process. The latter follows a $k^{-1}$ power-law, in
the energy conserving range in $k$ space.
