Review of Density Interface Inversion Method in Spatial Domain

Inversion of density interfaces using gravity data has traditionally been an important part of gravity research, and plays an increasingly important role in areas such as regional tectonic research and oil and gas exploration.The density interface inversion methods can be divided into the frequency domain and spatial domain methods according to different computing domains. The frequency domain inversion methods have been considered in previous literature. This paper briefly introduced the rationale and the advance of the direct iterative method, the ridge regression method and the regularization method,which are most studied and used among the spatial domain methods. The performance of the three methods showed that the inversion results of the direct iteration method and the ridge regression method are both the smooth shape density interfaces, while the regularization method can estimate the density interfaces of non-smooth morphology, and is convenient to add prior constraint information. The inversion results of density interface are greatly determined by the precision of potential field separation. The prior information should be used as constraints for gravity field separation as far as possible or the layer-by-layer separation technique could be adopted. The density contrast of the density interface also has noticeable impact on the inversion result. It is necessary to make full use of the rock density data to build a three-dimensional density contrast variation model that conforms to the tectonic features to improve the inversion accuracy.In terms of the theory of inversion method, it is also necessary to combine prior constraint information (which can be obtained through drilling and seismic data, etc.) to improve the accuracy of inversion.More importantly, it is necessary to define the corresponding relationship between the inverted density interface and the geological structure interface in order to evaluate the inversion results correctly.Finally, this paper discussed the developing trend and study emphasis for density interface inversion.The inversion methods that are suitable for large regional or global scale need to be studied with the rapid development of gravity observation technology and the diversification of research objectives. With the increasing difficulty of geological target exploration, it is also urgent to study the optimal single-density interface inversion method conforming to the tectonic features and develop the multi-layer density interface inversion method.