Cortical bone is a viscoelastic heterogeneous medium which may be assessed with axial transmission. This work aims at evaluating the average depth investigated by the lateral wave for radial variations of material properties in relatively thick cortical bone. The equivalent contributing depth (ECD) is derived from the finite element simulation results for spatial variations of a viscoelastic coefficient (eta(11)) and of porosity. A value of ECD equal to around 1.6 mm is obtained for a spatial variation of eta(11). The method fails to predict accurate values of the ECD for a spatial variation of porosity, because all parameters vary simultaneously. (C) 2011 Acoustical Society of America