The Study On The Processing And Interpretation Methods Of Magnetic Data Under Strong Remanent Magnetization

Geophysics exploration plays an impotent role in solving the geological issues.The continuous development geophysical instruments and detection technologies force the development of more stabilized and effective processing and interpretation method.Magnetic data are widely used in mineral exploration and geologic mapping.Transform the observed total magnetic intensity(TMI)anomaly into the source located in the north magnetic pole is the prerequisite of the traditional magnetic processing method.However,interpretation of magnetic data can be serious mislead by the presence of significant remanent magnetization components.This paper forces on multitype processing and interpretation methods under strong remanent,mainly including magnetic field edge detection method,magnetic field fast inversion method,and 3D inversion method.It adopts several suitable methods to solve the geological issues under strong remanence.The availability and precision of those methods are tested by synthetic models and the TMI data in Wudalianchi area.The results demonstrate those approaches are feasible.The TMI anomaly can be transformed to several quantities which are less likely affected by the direction of source magnetization including analysis signal amplitude(ASA),total magnitude(TM)magnetic anomaly,full tensor magnetic module(FTM),and normalized source strength(NSS).In comparison,the 3D ASA is not completely independent of the magnetization direction of the source.TM maintain more long wavelength information,but still affected by the remanence.FTM is less affected by the remanence.NSS is minimally affected by the remanence and has a linear relationship for the simple source.However,NSS removes the phase information content of the field.The inversion of NSS may not work well due to these losses.Magnetic field edge detection technology set an important role in the study of subsurface structure's feature and distribution.In order to choose the apparent methods that can be applied to the magnetic data containing remanence,this section tests and summarize the fundamental principle and feasibility of these methods including the total horizontal derivative(THD),vertical derivative,tilt angle and the normalized anisotropy variance method(NAV)based on those transformations which are less likely affected by remanence.The THD and the NAV of TM and FTM can detect geological boundary under unknown magnetic direction.Among them,the THD method based on FTM depicts the real boundary closest.The rapid inversion method can obtain the magnetic source type and distribution without pre-modeling.In turn,these preliminary result can be used for magnetic inversion.Applying the depth from extreme point(DEXP)method to NSS is proposed to estimate the horizontal and vertical position under strong remanence.The applications of 3D correlation imaging and Euler deconvolution under strong remanence are also summarized.The 3D correlation imaging approach for the TM and NSS are affected by the lateral horizontal magnetic source.Meanwhile,the application of DEXP method to NSS needs consider the lateral horizontal magnetic source with reverse magnetic direction,and at the higher altitudes,some artifacts will appear in NSS.Estimating the source location and structural index using Euler deconvolution of the NSS is a feasible approach.In practical applications,various types of rapid inversion methods can complement and constrain each other.The 3D physical inversion of magnetic data can quantify the distribution of the magnetic source.After preliminary understanding of distribution location,and burial depth by using edge detection method and rapid inversion method,the underground magnetic source will be quantitatively explained by 3D inversion.A spatial gradient weighting function was used to add prior information of geological bodies into the inversion algorithm,thereby constraining the geometry of the inversion result.Using the TM focusing inversion with the spatial gradient weighting function,the inversion results are consistent with the real model and have a higher accuracy.Finally,according to the above method,the workflow of the magnetic data under strong remanence was applied to the field data in the Wudalianchi area,and preliminary judgment was made on the magnetic anomaly morphology,fault structure information,magnetic source depth information,and magnetic distribution within the area.These results provide a reference for solving subsequent geological-geophysical problems.