Estimation of magnetization directions using a sequential approach with inversion of normalized source strength and Bayesian Monte-Carlo method

Total magnetization direction is not only an important parameter in magnetic data analysis, but also provides valuable insights into the magnetic mineral composition, structure, and evolution of its sources. However, this direction is often unknown in the presence of strong remanent magnetization. We developed a sequential approach comprising three steps to estimate the magnetization directions of sources. The spatial locations and shapes of the anomalous bodies are first determined using L 1 -norm inversion of normalized source strength (NSS). For each anomalous body, the three components of the magnetic anomalous vector are then obtained through a fast forward calculation based on Poisson's relation. A Bayesian Monte-Carlo inversion of total-field data is last employed to estimate the unknown magnetization directions of all anomalous bodies and their associated uncertainties. A synthetic model consisting of two causative bodies with distinct total magnetization directions was tested to validate this approach. Moreover, we analyzed the sensitivities of three magnetization parameters and comprehensively investigated the influences of several factors on the estimation results. A field data example using the total-field magnetic anomaly over the Black Hill Intrusive Complex was also studied. The results and analyses suggest that the proposed approach is applicable to sources containing multiple bodies with varying magnetization directions. In addition, supplementary prior information is advisable for cases where the inversion of NSS is not suitable in the first step, such as when the source body is located at great deep or has an asymmetric shape.