Research And Application On 3D Constrained Inversion Of Gravity And Magnetic Data

In the construction of gravity and magnetic property model, as not involved in complex shape changes and much easier to incorporate such priori information and constrains as geological data, property inversion has become the development tendency of gravity and magnetic inversion.In fact, the key of inversion technologies is to make full use of constrains to avoid non-uniqueness as much as possible. Therefore, this thesis takes a deep research on 3D constrained inversion of gravity and magnetic data, compares the ideal effect of constrained inversion on different models, and verifies the good effect of constrained inversion by processing practical field data.At first, based on the study of basic theory of gravity and magnetic anomaly, this paper concentrates on the research of computational method of point-source method about gravity and magnetic anomaly, obtains the forward discrete formula of point-source method, and realizes the gravity and magnetic anomaly forward computation of different models by compiling Fortran program.In the second place, on the base of being familiar with basic inversion theory, the article mainly studies the smooth constrained 3D inversion of gravity and magnetic anomaly proposed by Li and Oldenburg from University of British Columbia. In their inversion theory, the constructed objective function incorporates both the data misfit term and the model function term.The regularized parameter is to control the weighting of model functionin the objective function. The depth weighting is incorporated to the objective function in order to counteract the kernels’ natural decay with distance,i.e., skin effect. The roughness function is deduced and introduced to the model function and the smooth constrain of the model is realized. The conjugate gradient method, which is better than general inverse method, is employed to minimize the objective function.Furthermore, this thesis takes magnetic anomaly inverse as examples to design the following 4 models: one upright cuboid model, two upright cuboids model, five upright cuboids model and dipping slabs model. Such skills as depth weighting and model weighting are applied in the inversion. The inversion effects with or without depth weighting, with or without model weighting are analyzed to conclude that the recovered models with these constrains are closer to the real model.At last, the constrained inverse methods are put use to the practical gravity and magnetic exploration in Dongqiao area of Tibet. Good effect is obtained and the effectiveness of the methods are verified.