### Abstract

In this paper the locations where p_{app} = p_{1} 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 σ_{1}, σ_{2} 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 (p_{Re Z}, p_{Im 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 p_{app} and the phase φ are that they either satisfy p_{app} = P_{1} 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 P_{Re Z} and the φ_{MT} curves.

Original language | English |
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Pages (from-to) | 763-774 |

Number of pages | 12 |

Journal | Geophysical Prospecting |

Volume | 45 |

Issue number | 5 |

DOIs | |

Publication status | Published - Sep 1 1997 |

### ASJC Scopus subject areas

- Geophysics
- Geochemistry and Petrology