Analysis of Magnetotelluric Data Using the Reilly Decomposition Technique

Abstract

Results of magnetotelluric rncasurements madc ovcr coinplcx three-dimensional structures are usually expresses as an impedance tensor which has 8 independent components, all containing useful information. The Reilly (1979) decomposition technique rcprcsents thcsc 8 paramctcrs as an admittivity, which is thc sum of two rcal tensors: an apparent conductivity (or apparcnt rcsistivity) tcnsor, and an apparcnt permittivity tcnsor. Thc apparcnt permittivity can be used to illustratc thc phasc cliangcs associatcd with complcx structurcs. This dccompositioii is dcmonstratcd for an idcaliscd model of geothermal system. For this model, thc apparent resistivity tensor shows similar properties to the standard MT prcscntation tcchniqucs. Howcvcr, thc apparciit pcrinittivity tcnsor shows variations that appcar to delincatc thc modci boundaries with some precision. This decomposition may prove a uscful tool in the analysis of MT data in complex structures such as geothermal systems.