The response of perturbation and induction arrows to a three‐dimensional buried anomaly

A numerical model is employed to calculate theoretical perturbation and induction arrows for a spatially confined three‐dimensional (3-D) conductivity anomaly located at various depths below the surface of the earth for two source periods. The results indicate that the magnitudes of the induction arrow decrease as the anomaly depth increases and the arrows point toward the conductive anomaly even at great depth below the surface. It is found that the extent of the anomalous induced currents depends upon the depth of the inhomogeneity and on the source field period. The ([Formula: see text]) perturbation arrow can be used to outline the spatial extent of the anomaly, and the ([Formula: see text]) quadrature‐phase arrows better indicate the spatial extent than the in‐phase arrows if the source period is not an optimum one.