Study On Fast Joint Inversion Of Gravity And Vertical Gradient Data With Cross-constraint

With the development of gravity measurement technology,the high precision measurement of gravity and gravity gradient can be realized effectively.Compared with gravity gradient data,gravity data has more advantages in detecting deep field sources,while gravity gradient data contains more high-frequency information,which can better identify the boundary and the shape of shallow anomaly.The comprehensive utilization of gravity and gravity gradient data can effectively obtain the characteristics of the field sources at different depths and improve the resolution of the identification of the field source.At present,there are two main methods for the joint inversion of gravity and its gradient data: one is to place the two data in a matrix for the inversion,and the other is to use the cross-gradient method to achieve the joint inversion.It is difficult to measure and control the influence of the two kinds of data in the inversion of gravity data and gravity gradient data,and the resolution for the geological bodies of the previous joint inversion results is relatively low.This paper studies the joint inversion method of gravity data and gravity vertical gradient data in order to obtain high-resolution inversion results to process and interpret the data accurately.The joint inversion method with cross-constraint is proposed to obtain high-resolution density distributions at different depths.First,regularization inversion is used to the gravity and its vertical gradient data,respectively.Then,the two inversion results are normalized to form the cross-constraint.Finally,the cross-gradient method is used to realize the joint inversion of gravity data and gravity vertical gradient data with the structural constraints,and the cross-constraint is added to strengthen the constraints,so as to further improve the vertical resolution of the joint inversion.Through model test,the inversion results of the proposed method and the conventional method are compared,and the results show that the joint inversion method based on the cross-constraint has better resolution and anti-noise performance for the anomaly,which provides the theoretical support and ideas for the methods of the joint inversion of gravity and gravity gradient data.The proposed method is applied to the gravity and gravity vertical gradient data interpretation of Liaoyuan coal mine of Jilin province.The inversion result is consistent with the known ore field and corresponding with the section of the high-density resistivity.The position and the range of the gob are identified,which provides effective information for the exploration,so as to reduce the risk and cost.With the development of gravity measurement methods such as airborne gravity and satellite gravity,it is possible to obtain large-scale gravity data in large areas.It has become a difficult and hot issue to efficiently process and interpret the large-scale observation data.The wavenumber domain method is used to accelerate the forward modeling of an isolated subject.Based on the equivalence of regular grid and the properties of Toeplitz matrix,the multiplication of large matrices can be accelerated by fast Fourier transform from spatial domain to wavenumber domain,which improves the computational efficiency of inversion.In the process of the gravity exploration,there is largely undulated landform in the study area.The influence of the undulating terrain should be considered in order to ensure the precision of the inversion calculation.Undulating terrain inversion can be computed by two subdivisions: regular subdivision and irregular subdivision.Since the complex inversion calculation of irregular subdivision is not conducive to rapid calculation,this paper studies the fast joint inversion method with the cross-constraint of undulating terrain with regular subdivision.The undulating terrain data is conversed from curved-surface into horizontal-plane.The survey area is divided into regular grid subdivision with the highest point of the terrain to realize fast inversion calculation.For the study of the inversion under the undulating terrain condition,the application of the joint inversion method of gravity and gravity gradient data with cross-constraint is extended,which can better serve the interpretation of real data.The proposed method is applied to the satellite gravity data processing of Changbai Mountain to estimate the location and distribution of the magma chambers,and the magmatic route.The inversion results are in good agreement with the previous research results,which further verifies the practicability of the study on the cross-region volcanic system of the proposed method.