A new approach to depth determination from magnetic anomalies

Abstract

We have developed a semiautomatic method to determine the depth to shallow and deep‐seated structures from a magnetic anomaly profile. It involves using a relationship between the depths to two coaxial sources obtained by combining observations at symmetric points with respect to the coordinate of the sources center. For five established, fixed data points, the depth to the shallow structure is determined for each preassigned depth of the deep‐seated structure. The computed depths to the shallow structure are plotted against the computed depths to the deep‐seated structure, yielding a continuous, monotonically increasing depth curve. The spacing between the observations is then modified, producing several curves. The accepted estimates for the depths to both structures are read at the common intersection of these curves. The effective intensity and the angle of magnetization of both structures are also estimated. The proposed method was tested both on noisy synthetic and real magnetic data. In the case of synthetic data, the depth curves method determined the correct depths of both coaxial and laterally offset sources. In the case of practical data (vertical component anomaly over a chromite body in the Guleman concession, Turkey), the method suggested the shape of the buried shallow structure resembles a horizontal cylinder model buried at a depth of 31 m and the shape of the buried deep seated structure resembles a dike model buried at a depth of 62 m. The estimated shape and depth of the shallow structure are in very good agreement with the results obtained from drilling and surface geology. The area appears to still hold promise for chromite exploration from the deeper structure.