Chapter 3 Modelling electromagnetic fields in a 3D spherical earth using a fast integral equation approach

Abstract We present a numerical solution for the global induction problem. The solution calculates the electromagnetic fields in spherical three-dimensional (3D) earth models that are excited by external or internal currents. The models include a number of 3D isotropic (or anisotropic) inhomogeneities that reside in a radially symmetric section. The solution exploits the modified iterative-dissipative method. This fast integral equation approach allows the recovery of an accurate solution, even for large conductivity contrasts. In order to verify our solution we compare it with a staggered-grid finite-difference solution for a model with two (surface and mantle) laterally inhomogeneous conducting thin layers, and also with a Cartesian integral equation solution for a model with deep-seated local 3D anomaly. Both comparisons demonstrate very good agreement.

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