The magnetic anomaly caused by a buried dike is separated into its even and odd components, which have a simple symmetry with respect to the origin. These values an integrated up to the half-maximum abscissa for the even component, and the maximum abscissa for the odd component. The integration nomograms are generated using various values to the half-width and depth in the theoretical anomaly equations. These nomograms are used to determine the half-width and depth to the top of the dike for the field anomaly. The method also includes the determination of the index parameter (Q) and the amplitude coefficient (P). An example using theoretical data shows the effectiveness of the present method.