In this paper the locations where papp = p1 and φ = π/4 and where these parameters reach an extreme value in two-layer magnetotelluric (MT) sounding curves are summarized in an extremely compact form. The key parameters over two-layer models with conductivities σ1, σ2 and upper layer thickness h are the real S and α, where S is the conductivity contrast and a is the distance between the observation site and the conductivity interface, normalized to the half skindepth in the first layer. If the impedance components, various resistivity definitions (pRe Z, pIm Z and p|Z|, based on different parts of the complex impedance Z) and the magnetotelluric phase φ are derived as a function of S and α, then the conditions for the apparent resistivity papp and the phase φ are that they either satisfy papp = P1 and φ = π/4 or attain extreme values which can be given in terms of simple algebraic equations between S and α. All equations are valid for observation sites at any depth 0 ≤ z ≤ h in the first layer. The set of equations, presented in a tabular form, may make it possible to determine a layer boundary from the short period part of the sounding curves, in particular the PRe Z and the φMT curves.
ASJC Scopus subject areas
- Geochemistry and Petrology