Layer 1 (top)
Layer 2 thickness & basement
Apparent resistivity $\rho_a=\dfrac{1}{\omega\mu_0}|Z|^2$ and phase $\phi=\arg Z$, where the surface impedance $Z$ comes from the layered-earth recursion. For a 1D, isotropic Earth with this sign convention, phase above 45° commonly indicates decreasing resistivity with depth over the sampled interval; below 45° commonly indicates increasing resistivity.