  Graphene outstanding properties directly come from its pecular electronic
structure and thus from the honeycomb lattice symmetry. The way interaction
with the substrate impact this lattice is of primary importance. This is
peculiarly true for epitaxial graphene because of the SiC substrate. The
advantage of this system that produces macroscopic samples in registry with a
substrate could turn to a major drawback if the graphene lattice reveals to be
strongly distorted. Extensive ab initio calculations supported by Scanning
Tunneling Microscopy experiments, demonstrate here that the substrate indeed
induces a strong nanostructuration of the interface carbon layer. It propagates
to the above C layer where it generates incommensurate ripples in the honeycomb
lattice.
