Research And Application Of Gravity And Magnetic Interface Inversion Based On Variable Property Constraint

In order to solve the problem of environmental pollution and energy crisis in today's society,it is more and more urgent to find clean energy to replace traditional fossil energy.The distribution of underground temperature field can not be obtained by direct measurement for geothermal resources buried deep underground,so it is very difficult to evaluate the exploration process.Nowadays,geophysical methods are mainly used in geothermal exploration,and the distribution characteristics of underground temperature field can be obtained indirectly by measuring the changes of geophysical parameters.Generally,the magnetic properties of the stratum will increase and decrease with the increase of temperature everywhere,resulting in the complete disappearance of the magnetic properties of the stratum at a certain depth underground.The temperature interface at this depth is called indwelling,and its distribution pattern directly reflects the distribution characteristics of the underground temperature field.The Moho surface is another important physical interface,and its uplift will result in crust thinning,uplift of upper mantle and upwelling of hot material in mantle,providing deep heat source for the formation of geothermal.The study of Curie and Moho surface inversion has important guiding significance for geothermal field evaluation.At present,the inversion methods of the interior and Moho surfaces are mainly the Parker-Oldenburg inversion method,but the Parker-Oldenburg algorithm has problems such as the selection of physical parameters,model assumptions and iterative convergence.In this paper,a two-interface model,vertical variability parameters and a new polynomial iterative algorithm are introduced to constrain the Parker-Oldenburg interface inversion process.Through numerical simulation and comparative experiment,the influence of the improvement made in this paper on the inversion results is explored.The research work is mainly divided into two parts: 1)the influence of the introduction of variable susceptibility factor on the inversion results under the same algorithm application condition is studied;2)study the influence of the introduction of new iterative algorithm on the inversion results under the same model application condition.The numerical simulation results show that the traditional Parker-Oldenburg method presents such problems as low inversion accuracy and non-convergence in the calculation process.Compared with the traditional Parker-Oldenburg method,the proposed method improves the calculation efficiency by more than four times,reduces the error by nearly two orders of magnitude,and the inversion results have better convergence and inversion accuracy.In terms of application examples,combined with the gravity and magnetic anomalies of Songliao basin and Gonghe basin,the algorithm described in this paper is applied to the calculation of the habitat and Moho surface of Songliao basin and Gonghe basin.Based on the known physical parameters of basin basement depth and vertical variation,a two-interface model was established for basin basement and surface,and the forward modeling formula of related anomalies was combined to obtain the forward modeling anomalies of basement and overlying strata.The forward modeling anomalies were removed from the total anomalies and the remaining regional anomalies reflecting the deep interface were extracted.The distribution characteristics of residual magnetic anomalies in Songliao basin reflect that the EW trending structure in the early deep part of Songliao basin is disturbed and faulted by the NS trending structure in the later deep part of Songliao basin.The distribution characteristics of residual magnetic anomalies and residual gravity anomalies in Gonghe basin highlight the basin margin,reflecting that Gonghe basin and surrounding areas are controlled by NW trending faults,and the basin is controlled by NE trending faults,reflecting the complexity and superposition of the geological structure of Gonghe basin.The residual anomalies mentioned above can be regarded as generated by a two-interface model composed of basements and deep underground interfaces,and the residual anomalies can be used for indwelling and Moho surface inversion calculation with the method described in this paper.The indwelling inversion results of Songliao basin show that the central and northern part of the basin is an indwelling uplift area,and it is speculated that the indwelling uplift in this area is related to the upwelling of mantle heat plume.The inversion results of the Moho surface in Songliao basin show that the Moho surface in the middle part of the basin is uplifted and the crust is thin.The distribution pattern of the inner habitat of Gonghe basin reflects the complexity and superposition of the geological structure of Gonghe basin.The inversion results of the Moho surface in Gonghe basin have a good correspondence with the geological structural units in Gonghe basin and its surroundings.The results show that the Moho surface in Gonghe basin is uplifted,the crust is thin,and the upwelling of mantle provides deep heat source for Gonghe basin.