Hybrid method for 3D modeling of electromagnetic fields in complex structures with inhomogeneous background conductivity

We present a new formulation of the hybrid method for threedimensional (3D) electromagnetic (EM) modeling in complex structures with inhomogeneous background conductivity (IBC). This method overcomes the standard limitation of the conventional IE method related to the use of a horizontally layered background only. The new method allows us to compute the effect of IBC structures by using any appropriate numerical method which may be able to build a model with a flexible grid. This approach seems to be extremely useful in computing EM data for multiple geologic models with some common geoelectrical features, like terrain, bathymetry, or other known structures. It may find wide application in inverse problem solution, where we have to keep some known geologic structures unchanged during the iterative inversion. The method was carefully tested for modeling the EM field for complex structures with known variable background conductivity. The effectiveness of this approach is illustrated by modeling marine magnetotelluric (MT) data.