Abstract

A method of analyzing the tensor nature of magnetotelluric fields from short independent sections of filtered MT data is presented in which: (1) horizontal field components are filtered at chosen periods; (2) short sections which show a well defined signal over 3-4 cycles are selected from the records; (3) the polarizations of these short record sections are plotted; and (4) Fourier coefficients calculated for section pairs showing differing magnetic field polarizations are then used to calculate the elements of the impedance tensor. Results of this analysis performed on MT field data show that the use of MT signal pairs yields uniform principal resistivities for calculations using several different section pairs of the same period. These results also illustrate internal consistency of the resistivity estimates over the complete period range of the data (30-7500 sec). A brief comparison of the MT pairs calculations and results derived from a least-squares approach at a selected period shows good agreement between the two methods. The overall results suggest that the use of independent signal pairs in the determination of the tensor impedance could complement more traditional methods in some cases.

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