  Space-time fractional Zener wave equation, describing viscoelastic materials
obeying the time-fractional Zener model and the space-fractional strain
measure, is derived and analyzed. This model includes waves with finite speed,
as well as non-propagating disturbances. The existence and the uniqueness of
the solution to the generalized Cauchy problem are proved. Special cases are
investigated and numerical examples are presented.
