3D gravity inversion in frequency domain based on mixed L1+L2 norm
3D gravity inversion has been widely used in mineral resources exploration and research on deep density structures.However,traditional 3D gravity inversion methods in spatial domain suffer low depth resolution,severe non-uniqueness and low computational efficiency,which affect the accuracy and reliability of geological interpretation.Aiming at the above problems,this study proposes a 3D gravity inversion method in frequency domain based on a mixed norm regularization constraint.We firstly construct a model objective function based on depth weighting and L1+L2 mixed norm constraints,and apply the frequency domain method of 3D gravity forward modeling to each iteration of an inversion to update the model so that the problems of storing and computing the dense Jacobian matrix in traditional spatial domain inversion methods are transformed into frequency domain forward modeling,which greatly reduces the computational time and memory occupation.To ensure high accuracy of the frequency domain forward method,the high-precision Gaussian numerical integral is used instead of the rectangular integral in traditional Fast Fourier Transform(FFT)algorithm.Two synthetic inversion examples show that the proposed inversion method can effectively reduce the"skin effect"and smearing phenomenon and can recover more complex geological models compared with the traditional spatial domain inversion methods based on L2 norm regularization and L1 norm(focused)regularization.Finally,we apply this method to 3D density imaging of the Mobrun sulfide body in Noranda,Quebec,Canada.The results show that the depth of the sulfide body ranges from～15 to 170 m,consisting with previous borehole data,which proves the effectiveness of the proposed method.
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