The Application of Theta Method to Potential Field Gradient Tensor Data for Edge Detection of Complex Geological Structures

Edge detection of magnetized structures is an important application of magnetic filters for geological interpretations. In this way, one can mention methods of the potential field derivatives which are categorized into: methods based on scalar potential field and potential field gradient tensor (PGT) data. Using five independent signal components, methods based on the PGT matrices have higher accuracy than methods based on scalar potential field data. Investigations of various methods of edge detection show that as geologic conditions become more complex, they greatly lose their efficacy and sometimes suffer from distortions. These distortions probably result from the Gibbs phenomenon which occurs in the process of computing the potential field data derivatives. This phenomenon creates false edges and incorrect interpretations of data. The theta(PGT) method addresses this phenomenon by combining the PGT matrix and the previously derived theta map method. The maximum value of theta(PGT) delineates the horizontal edge of geologic contacts. Achieved results by applying the theta(PGT) method on simple and then complex synthetic magnetic models demonstrates higher accuracy of the proposed method in comparison with the analytic signal, theta and horizontal directional theta (HDT) methods. The new method has no sensitivity to depth and strike, and also doesn't create additional edges. Furthermore, it has lower noise sensitivity and significantly reduces the effect of the Gibbs phenomenon. Finally, applying this method on real magnetic data from the Varzeghan area, northwest Iran, with respect to other methods reveals more details of structures in the area and characterized false faults resulting from the Gibbs phenomenon.