The Apparent Anisotropy of the SEG-EAGE Overthrust Mode

The Earth interior contains heterogeneities at all scales, ranging from pores and mineral grains to major global units. On the contrary, seismic recordings only contain variations larger than the minimum wavelength λmin. The heterogeneities smaller than λmin are naturally smoothed by the wavefield, leading to effective media when inverting seismic recordings to image the Earth. In particular, oriented small-scale structures lead to apparent anisotropy. In the present work, we apply the non-periodic homogenization method to the SEG-EAGE overthrust model to get the effective properties of a typical subsurface medium and to estimate the magnitude and the symmetry of the apparent anisotropy. We show that such anisotropy can reach 18%, most of it being explained by locally-tilted transverse isotropy. We also show that using the effective properties within an anisotropic wave simulator considerably decreases the computation requirement with respect to a wave simulation in the original model.