Research On Inversion Method Of Constrained Variable Density Gravity Interface In Complex Structure Area

Gravity density interface inversion in complex tectonic areas has always been an important part of geophysical inversion problems.The fluctuation of density interface is of great significance to the study of regional geological structure distribution and tectonic movement.The complex structure area has complicated geological conditions,and the underground density is unevenly distributed horizontally and vertically.It is not suitable for inversion with constant density inversion.The classic frequency domain density inversion method can realize variable density inversion in the vertical direction by changing the density function.But in the horizontal direction,variable density inversion cannot be performed according to the spatial distribution of different structures.In view of this situation,this paper studies the spatial domain cubic polynomial variable density interface inversion method that can take into account both lateral and vertical density changes,conducts theoretical model tests and applies it to the Moho surface inversion in the South China Sea.The main contents are:(1)In view of the uneven distribution of underground density in the horizontal and vertical directions,the study is divided into different areas based on geological and geophysical data in the horizontal direction,and the collected seismic sounding profiles are segmented in the vertical direction The velocity-density conversion formula is processed to obtain the discrete points of the depth-density difference,and the cubic polynomial variable density model of each region is fitted according to the different regions;(2)For the multi-solution problem of inversion,seismic surveys are added to the inversion Deep data is used as constraint information.Because the source of seismic sounding profiles is different,the seismic sounding data is adjusted by the cross-line method to improve the accuracy of the constraint information;(3)When inverting the Moho surface in the South China Sea The forward effect of the exponential variable density model is used to strip the gravity effect of the sediment layer,and then the high frequency interference of the shallow part is removed by the regularization filtering method to obtain the gravity anomaly of the Moho surface in the South China Sea;(4)Using the adjusted sounding data of the South China Sea as constraints,the depth of the Moho surface in the South China Sea was calculated using the cubic polynomial variable density interface inversion method,and the density parameters directly related to the inversion results were uncertain.Analysis,combined with seismic sounding data,analyzed and evaluated the inversion results,and discussed the selection of the optimal inversion results;(5)according to the optimal inversion results,the overall distribution of the Moho surface in the South China Sea The characteristics were analyzed,four profiles were extracted from the inversion results,the relationship between the Moho depth and different structural units was studied,and the geological structures in the South China Sea were divided according to the inversion results and other geological and geophysical data.