A Comparison of impedance invariants and GB decomposition method for magnetotelluric data analysis; A Case study from SW Iran

Dimensionality and distortion analysis of the measured magnetotelluric (MT) data are challenging procedures to conclude the main properties of regional geo-electric structure (e.g., its strike direction) and quantify the influence of superficial distorting bodies. In this paper, we applied several analysis methods to the same data set from southwest Zagros to determine the dimensionality and degree of the inherent distortion in the data and to recover the regional responses. Results show that the regional 2D responses can be better retrieved in a two-step procedure: First, the dimensionality and distortion are classified by impedance invariants and then, the Groom-Baily (GB) method is applied to remove distortion effects and to estimate the regional strike and principal impedances. An audio-magnetotelluric (AMT) data set acquired at 19 stations along a profile in the southwest of Simply Folded Belt (SFB) of the Zagros Mountains is investigated. The Bahr and WAL invariants confirm regional 1D and 2D structures with local galvanic distortion at most periods. The GB decomposition of MT impedance data reveals period-independent distortion parameters. The strike analysis on all data whose principal phase differences are greater than 5˚ shows a regional trend of about 30˚. 2D inductive effects were also retrieved by removing distortion effects from the measured data.