Comparison study of magnetotelluric inversion using different transfer functions.

摘要

Near-surface inhomogeneities (NSI) are a major problem that distorts magnetotelluric (MT) data. In this thesis, I have developed a method of 3D inversion of MT data based on the phase-tensor approach. Theoretically, unlike conventional MT apparent resistivities, the phase-tensor data are not distorted by the near-surface inhomogeneities and thus should provide more reliable information about deep geoelectrical structures. I have derived the relationships between Frechet derivatives of the phase tensor and those of the MT impedance components. Once the sensitivities are known, the method closely follows Consortium for Electromagnetic Modeling and Inversion's (CEMI's) 3D MT inversion algorithm, which is based on the integral equation (IE) formulation of EM field equations and receiver footprint approach. In this thesis, I conduct a comparison study of 3D MT inversions, using impedance tensor and phase tensor methods. I present a case study using the MT data from the McArthur River area. The results from the impedance tensor compared well with the results from other publications. The phase tensor results did not compare well with any other results. This indicates that the phase tensor method, being theoretically very robust to near-surface distortions, in practice does not work as well as one would expect. I explain this phenomenon by the significant effects of noise in the field MT data on the components of the phase tensor.