Forward and adjoint simulations of seismic wave propagation on fully unstructured hexahedral meshes by Peter, D, Komatitsch, D, Luo, Y, Martin, R, Le Goff, N, Casarotti, E, Le Loher, P, Magnoni, F, Liu, Q, Blitz, C, Nissen-Meyer, T, Basini, P, Tromp, J