A General Framework for 3D Interpretation of Magnetic Data Affected by Remanence and Self-Demagnetization

3D inversion of magnetic data has been successfully used in many aspects of geophysical exploration over the last decade. In a majority of cases, one can assume that the direction of magnetization is the same as the current inducing field direction, and generalized magnetic inversions requiring this information typically perform well in recovering susceptibility distributions. However, the sometimes unknown direction of total magnetization, caused either by the presence of high magnetic susceptibility or remanent magnetization, has limited the use of this technique. We present a general framework for solving these problems by examining the three classes of magnetization and formulate a suite of methods of practical utility in any magnetic environment. The first class performs inversion for the case of induced magnetization with weak magnetic susceptibility, where the magnetization direction is the same as the Earth’s inducing field. The second class focuses on the estimation of total magnetization direction when the field is not purely induced, and then incorporates the resultant direction into an inversion algorithm that assumes a known direction. The final class focuses on the direct inversion of the amplitude of magnetic anomaly vector, a quantity that depends weakly upon magnetization direction. With these new developments, we show that it is now feasible to invert any magnetic exploration data set, regardless of whether it is purely induced, or affected by strong remanence or self-demagnetization.