  We consider an unbounded lattice and at each point of this lattice an
anharmonic oscillator, that interacts with its first neighborhoods via a pair
potential $V$ and is subjected to a restoring force of potential $U$. We assume
that $U$ and $V$ are even nonnegative polynomials of degree $2\sigma_1$ and
$2\sigma_2$. We study the time evolution of this system, with a control of the
growth in time of the local energy, and we give a nontrivial bound on the
velocity of propagation of a perturbation. This is an extension to the case
$\sigma_1 < 2\sigma_2-1$ of some already known results obtained for $\sigma_1
\geq 2\sigma_2-1$.
