Magnetotelluric tensors, electromagnetic field scattering and distortion in three‐dimensional environments. Issue 10 (28th October 2016)

• Record Type: Journal Article
• Authors: Brown, Colin
• Is Part Of: Journal of geophysical research. Volume 121:Issue 10(2016:Oct.)
• Page Start: 7040
• Page End: 7053
• Publication Date: 2016-10-28
• Subjects: apparent resistivity tensor -- extended Born -- EM migration -- extended phase tensor; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2016JB013035
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: This paper describes how subsurface resistivity distributions can be estimated directly from the magnetotelluric (MT) tensor relationship between electric and magnetic fields observed on a three‐dimensional (3‐D) half‐space. It presents an inhomogeneous plane wave analogy where relationships between horizontal electric and magnetic fields, and an apparent current density define an apparent resistivity tensor constructed from a quadratic function of the MT tensor. An extended‐Born relationship allows the electric field to be normalized with respect to an apparent background current density. The model is generalized by including the vertical magnetic field in a 3 by 3 MT response tensor. A complex apparent wave number tensor, constructed from this tensor, has eigenvalues which, using the plane wave analogy, are the vertical wave numbers associated with the eigenpolarizations of propagating waves in the model half space. The elements associated with the vertical magnetic field transfer function define the horizontal wave numbers. An extended 3 by 3 phase tensor contains four elements of the conventional 2 by 2 phase tensor and two elements associated with the vertical magnetic transfer function. The extended phase tensor and a single real distortion tensor with six independent elements can be used to quantify static electric and magnetic field distortions. The approach provides a theoretical basis for visualization and migration of MT data, in comparison with results from other electrical and EM techniques, a starting point for constrained 3‐D inversions, and an assessment of results with other geophysical and geological data. Key Points: An apparent resistivity tensor allows visualization of MT data suited for geological interpretation A wave number tensor allows the computation of apparent horizontal and vertical wave numbers for MT A phase tensor and a distortion tensor, each with six elements, quantify static EM field distortions