Abstract: In seismic exploration, interbed deposits occur as thin layered or interbed formations which are typically described as anisotropic media or transverse isotropic media at long wavelengths.Based on a review of theoretical developments, numerical simulations, and physical experiments, it was found that very strict conditions need to be met to evaluate an equivalent anisotropy.In particular, for a rhythmic thin interbed, the ratio of the wavelength to the thickness of the interbed needs to be at least ten.For a stochastic thin interbed, the average length needs to be much larger than the thickness of the individual layers and much smaller than the main wavelength.Additionally, it was found that the equivalent anisotropy of a rhythmic thin interbed is closely related to the ratio of the wavelength to the thickness of the interbedded unit or layer, but also to the difference in physical property of thin reservoir.Finally, to evaluate an equivalent anisotropy for a stochastic thin interbed, the relationships among the average length, inhomogeneity scale, and main wavelength need to be accounted for.