Inversion Strategy
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Inversion Strategy
The past decade witnessed the striking technological and methodological advances in exploration and academic magnetotellurics. Field equipments ensuring a stable determination of magnetotelluric and magnetovariational response functions have been worked out. Effective programs have been developed for 1D, 2D and even 3D inversions of impedances and tippers. Magnetovariational sounding, for many years considered as an assistant in localizing and identifying the geoelectric structures, has been put in the forefront of the modern magnetotellurics. It became a powerful tool for resolving and studying the horizontal and vertical conductivity distribution without static shift problem. New approaches to the analysis and interpretation widening the informativeness of geoelectrics have been proposed. Field investigations have been conducted in many tectonic provinces of the world providing basically new information on the Earth’s crust and upper mantle that essentially supplements the results obtained by seismics. All these results need to be systemized and generalized. The development of a modern philosophy of the magnetotelluric interpretation is a challenge of current research. Nowadays we already have some works responding to this challenge. On the geophysical bookshelves we find monographs considering the methods of regularized solution of inverse problems based on the ideas of Tikhonov (Zhdanov, 2002; Berdichevsky and Dmitriev, 2002) and examining the technological and geological aspects of magnetotellurics (Simpson and Bahr, 2005). In the present monograph, we would like to focus our attention on the strategy of the integrated multicriterion inversion of the magnetelluric and magnetovariational response functions.
12.1 The Smoothing and Contrasting Inversions In general, we can consider two types of conductivity distributions (x, y, z): (1) a smooth distribution (x, y, z) that is continuous with its gradient, (2) a contrasty distribution (x, y, z) that has discontinuities. Let an inhomogeneous body, smooth or contrasty, be buried into the homogeneous Earth. It manifests itself at the Earth’s M. Berdichevsky, V.I. Dmitriev, Models and Methods of Magnetotellurics, C Springer-Verlag Berlin Heidelberg 2008 DOI 10.1007/978-3-540-77814-1 12,
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surface in a smoothed diffusive magnetotelluric anomaly with extent that can considerably exceed the body dimensions. The resolution of the magnetotelluric and magnetovariational soundings is such that we cannot distinguish the smooth body from the contrasty one. In view of errors in the initial data, both − distributions are equivalent. To decide between the smooth and contrasty − distributions, we need a priori information or some hypotheses. In regions with sufficiently slow horizontal variations in the conductivity and thickness of the geoelectric layers, we can take a quasi-homogeneous layered interpretation model and regularize the magnetotelluric and magnetovariational inversions by smoothing the solution obtained. Th
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