Validity of the dispersion relations in magnetotellurics: Part I—theory

Application of the dispersion relations (DR) in magnetotellurics (MT) is an efficient tool of post-processing and quality assessment of broadband field data. The main limitation of the approach is that it requires the observed transfer functions to be causal and minimum-phase (MP), which is formally secured only for 1-D and some types of 2-D impedances. As a consequence, many MT practitioners involuntarily restrict the DR application to apparent resistivity curves acquired in relatively simple geological conditions. In the present research, we show how an inherently non-MP or non-causal transfer function could be recognized, and propose a universal technique, which makes it possible to correctly apply the DR virtually to any set of field MT data.[Figure not available: see fulltext.].