Strategy Research On Joint Inversion Of Magnetotelluric And Gravity Based On Wide-range Physical Properties Constraints

Joint inversion,which can reduce the limitation of a single geophysical method and the non-uniqueness of inversions,is a frontier of the field of geophysics.The wide-range petrophysical constraints has advantages of easy implementation,certain fault tolerance,and is weak dependence on the prior information.However,there are still the following problems:This technology is currently only implemented in the simulated annealing algorithm.There is no clear strategy to extend it into other nonlinear and linear optimization algorithms,which directly affects the promotion of the thinking of wide-range petrophysical constraints.In addition,Gramian constraints is low dependence on the prior information,but is low utilization on explicit relationship of physical properties.Based on this,we propose the wide-range petrophysical constraints strategies,which are suitable for nonlinear and linear optimization algorithms respectively,namely "petrophysical relationship + re-search" and "petrophysical relationship + range constraints + coupling term",and achieve some new techniques for joint inversions: Firstly,the joint inversion of magnetotelluric(MT)and gravity based on the differential evolution(DE)algorithms with wide-range petrophysical constraints thinking.Specifically,we take the improved DE algorithm with dual population structure proposed in this paper as an example,realize the re-search of physical properties within a certain range by introducing of petrophysical relationship and combining with the crossover and mutation operations of the algorithm;Secondly,the joint inversion of MT and gravity based on conjugate gradient algorithm using Gramian constraints with wide-range petrophysical constraints thinking.Specifically,we take the conjugate gradient algorithm as an example,introduce the Gramian coupling term into the objective function of the joint inversion,discuss two schemes which can limit the physical properties in a certain range,then,the prior petrophysical relationship is introduced into the joint inversion.Finally,the new geophysical joint inversion technology proposed in this paper is applied to the processing of MT and gravity field data from the Chating copper-gold deposit in Anhui province.Model tests show that: Firstly,the wide-range petrophysical constraints strategies proposed in this paper are feasible and have a high potential for promotion;Secondly,compared with the traditional DE algorithm,the improved DE algorithm in this paper has faster convergence speed and stronger optimization ability,in addition,the DE joint inversion based on the wide-range petrophysical constraints thinking,to some extent,is appropriate for the condition of the prior information is not precise,the non-perfect common interface of physical properties;Thirdly,the penalty function method is more suitable to the wide-range petrophysical constraints strategy using a linear algorithm,in addition,the conjugate gradient joint inversion using Gramian constraints based on the wide-range petrophysical constraints thinking,can improve the utilization of the prior petrophysical relationship,and improve the coupling of physical properties in a certain range;Finally,the field data processing of the Chating copper-gold deposit in Anhui province,verify the spatial distribution of the deposit in the shallow,the rootless granite porphyry at the Daoshancun reverse fault is the result of the nappe structure,delineate the spatial distribution of the deposit in the depth.