Approaches Of Gravity And Magnetic Rapid 3D Imaging And Variable Density Interface Inversion For Deep Detection

Gravity and magnetic methods are two popular tools for detecting deep structure and tectonic features.3D physical-property inversion and density interface inversion are two important tools for gravity and magnetic data interpretation,which have been playing significant roles in tectonic studies,mineral and energy exploration,hazard prevention and mitigation,and so on.The conventional space-domain 3D physical property inversion approach requires a large amount of physical memory and computation,which is not suitable for fast 3D inversion of large-scale data.The frequency-domain 3D imaging approach can realize rapid imaging and evaluation of largescale data,but its depth resolution is relatively low.The conventional density interface inversion approach under Cartesian coordinate system is not applicable to large-area or global studies.Furthermore,the routine approach under spherical coordinate system is not feasible to the ground observation data,and it neglects the density variations vertically and horizontally underground.Aiming at the above technique questions,we develop the approach of rapid 3D imaging for largescale gravity and magnetic data and the approach of variable density interface inversion under spherical coordinate system for the ground observation data.Our approaches will provide technique supports for rapid 3D geological evaluation and tectonic studies in deep detection.The main researches and achievements of this study are as follows:(1)On the basis of theoretical derivation,the frequency-domain approaches for 3D forward modeling and quasi-3D forward modeling of both gravity and magnetic anomalies and their gradients are presented.The synthetic data test shows that the accuracy of our approaches is equivalent to that of the analytic solution in space domain,while the efficiency of our approaches is much higher than that of the space-domain algorithm.Therefore,of our approaches are suitable for rapid forward modeling of large-scale model.(2)Through theoretical derivation and the involution of depth-scale factor and constraints of physical-property range and interface depths along with the iterative optimization algorithm,the frequency-domain approach for 3D imaging of both gravity and magnetic anomalies and their gradients are presented.The synthetic and real data tests reveal that the efficiency of our approach is much higher than that of the conventional space-domain physical-property inversion algorithm.Furthermore,the depth resolution of our approach is better than that of the common frequencydomain imaging approach.Our approach is suitable for rapid 3D imaging and evaluation of largescale data.(3)Based on the theoretical derivation and the improvement of Gauss-Legendre integral algorithm,the approach for forward modeling of variable density interface under spherical coordinate system is presented.The synthetic data tests demonstrate that our approach can effectively improve the forward modeling accuracy on the ground observation surface,which is suitable for the variable density interface forward modeling of large-area on ground observation surface.(4)The variable density interface inversion approach under spherical coordinate system is given by using the iterative optimization algorithm.The synthetic data tests show that our approach is effective and suitable for the variable density interface inversion of large-area and ground observation data.(5)The depth distribution of the lithospheric bottom interface(LAB)in Chinese mainland is obtained by using our approaches of variable density interface forward modeling and inversion under spherical coordinate system.The results indicate that the lithospheric thickness of Chinese mainland is thick in the west and thin in the east bouned by 110°E,and it ranges from 60 km to260 km as a whole.