On inhomogeneity parameters for Backus average

In this paper, we discuss five parameters that indicate the inhomogeneity of a stack of parallel isotropic layers. We show that, in certain situations, they provide further insight into the intrinsic inhomogeneity of a Backus medium, as compared to the Thomsen parameters. Additionally, we show that the Backus average of isotropic layers is isotropic if and only if $γ=0$. This is in contrast to parameters $δ$ and $ε$, whose zero values do not imply isotropy.