DISCUSSION

The results obtained here and in particular (arearranged) and (Pwavep) show in general terms that Thomsen's parameter $\epsilon$ is smallest when the variation in the layer $\lambda$ Lamé parameter is large, independent of the variation in the shear modulus $\mu$. This result is therefore important for applications to porous layers containing pore fluids for which Gassmann's (1951) equation shows that the effects of fluids influence only the $\lambda$ Lamé constants, not $\mu$. Similarly, we find that $\delta$ is positive in finely layered media having large variations in $\lambda$.Thus, the regions of positive but small $\epsilon$ when occurring together with positive $\delta$ may be useful indicators of rapid spatial changes in fluid content in the layers. This result cannot, however, be considered in isolation, as there may be other effects in nonlayered media that produce similar values of the Thomsen parameters, and these should be explored and enumerated before any definitive statement can be made.