Series and parallel transformations of the magnetotelluric impedance tensor: theory and applications

• Published in: Physics of the earth and planetary interiors 2005-05, Vol.150 (1), p.63-83
• Main Authors: Romo, José M., Gómez-Treviño, Enrique, Esparza, Francisco J.
• Format: Article
• Language: English
• Subjects: Impedance tensor; Magnetotelluric inversion; Magnetotellurics; Series and parallel transformation
• ISSN: 0031-9201; 1872-7395
• DOI: 10.1016/j.pepi.2004.08.021

The basic magnetotelluric (MT) impedance tensor transforms into a set of physical and geometrical parameters that maintain their validity regardless of dimensionality. In two dimensions (2D), the traditional TM and TE impedances rearrange into an equivalent pair, series and parallel, which complement each other and together represent the original tensor. The series equivalent relates to TM and the parallel counterpart to TE. We show how the series- and parallel-impedance concepts can be applied in three dimensions (3D), overcoming some of the current limitations of TE and TM 2D concepts. The series response function is mainly affected by galvanic effects related with current flow across interfaces, while the parallel impedance is more sensitive to inductive effects associated with current flow along interfaces. An intrinsic and most convenient property of the series and parallel impedances is that they do not depend on the measuring axes, as do the individual tensor elements, as well as the TE and TM impedances in the 2D case. The directional sensitivity of the new representation is provided by two angular parameters that complete the equivalency. Formally, a forward transformation operates over the original tensor elements in the traditional x– y domain, and produces parameters in what can be called the S–P domain, where S stands for series and P for parallel. The existence of the inverse transformation for going from the S–P to the original x– y domain guaranties that there is no loss of information when going from one representation to the other. We illustrate the performance of S–P quantities using forward computations on multi-dimensional models and 2D inversions of synthetic and field data.