The Research And Application Of Variable Density Interface Constraint Inversion

Density interface inversion by gravity anomaly is an important issue in the processing and interpretation of the gravity potential field. Calculation of the fluctuation or depth variation of density interfaces plays a critical role in regional tectonics research and petroleum exploration. Northeastern China,contains many Meso-Cenozoic basins, including the Songliao Basin. It is one of significant Petro1 eum industrial bases and has broad exploration prospects.we perform the research on 3D variable density interface joint inversion of gravity data and seismic data. The main results are summarized as follows:Firstly, as the strata density is heterogeneous both horizontally and vertically, we carry out the study of 3D variable density interface inversion. Based on the Fourier transform, the Parker-Oldenburg formulas in the frequency domain was extended for the three-dimensional case where the density changes with depth. From this, a gravity interface inversion formula was derived in which the assumed density can be varied laterally and vertically. Iterative convergence is assured by fixing a particular depth as the datum plane below the surface to reduce the interface fluctuation.Secondly, to solve potential multiple solutions for potential field inversion, we establish the joint inversion objective function, using known information to constraint inversion process. A priori information such as the depth of a known point can be incorporated into the iteration process to minimize potential multiple solutions for potential field inversion.Thirdly, to solve depth resolution of gravity data, we import a depth weighting function to distribute the interface with depth. Depth weighting is used to counteract the natural decay of the kernel so that the inversion yields depth information. This method can effectively correct interface distortion, which is applicable to large fluctuations of the interface.Fourthly, we analyzed the characteristics of the Bouguer gravity anomalies of Northeastern China. We then did multi-scale anomaly separation by using the preferential filtering method and obtained the regional anomaly produced by the Moho interface.Fifthly, with constraints of the scattered Moho depth information deduced from the seismic detection, the the regional gravity anomaly was inversed by using constraint variable density interface inversion to botain the Moho depth distribution of Northeastern China. Based on the gravity data and the corresponding other geological and geophysical data, we further studied the fault distribution in Northeastern China.