ABSTRACT

We have developed a new method of cascade three-dimensional (3-D) magnetotelluric (MT) inversion which combines the advantages of the rigorous and approximate methods. As the main engine of the inversion algorithm we use the quasi-analytical (QA) approximation of the forward modeling operator. In order to obtain a rigorous solution of the inverse problem, however, the inversion is implemented as a sequence of iterative processes (cascades). As a result, we constructed a rapid but rigorous inversion method which could be used for 3-D inversion of the array magnetotelluric data within a few minutes on a PC. The effectiveness of the method was demonstrated on a synthetic model. The case study includes the interpretation of an (MT) survey conducted by Phoenix Geophysics for mineral exploration near Rainy River in Ontario, Canada. It was demonstrated that this code produces a reasonable volume image of subsurface geological formations corresponding well with the drilling results.

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