| The density and magnetization of rock are closely related to the lithology and tectonics. Therefore, the study on the density and magnetization of rock is very significant for the interpretation of potential anomaly data, tectonic unit division and mineral resources investigation. The calculating of rock density and magnitization according to potential anomaly is called physical properties inversion of potential anomaly. Because of potential superposition and equivalence principle, the research of physical properties inversion has been an interested and difficult problem at home and abroad.At present, there are two main methods to inverse the physical properties of potential anomaly, such as optimization method and non-linear method. The algorithms of these two methods include Gauss algorithm, the steepest descent algorithm, Marquardt algorithm, singular value decomposition algorithm, ridge regression algorithm, the Back Propagation algorithm of artifical neural networks, genetic algorithm method and simulated annealing algorithm et al. The basic thinking of present methods is to divide the subsurround field sources region into many rectangular blocks with known shape and unknown density or magnetization. At first, initial values of density or magnetization are given. Then, the changed values of density or magnetization are needed to be gained. Finaly, the reasonable physical properties values that make the L1 norm or L2 norm of the difference between theory forward anomaly data and observed data to be least are obtained.Even though the present methods are reasonable and feasible in theory, there are still many problems in practice. There are mainly two problems about optimization method. Firstly, the establishment of large linear algebraic equation is needed, it consumes large computer memory and long computation time. Secondly, the equation is ill-conditioned and solution is unstable. The main problem of non-linear inversion methods is the long calculating time cosuming and large memory occupying when the quantities of inverse data are large. Overall the present inversion methods are ineffective during inversion of potential data, especially 3-D physical properties inversion in the large area due to the restriction of memory and computing velocity of computer.This paper presents a rapid method for 3D physical properties inversion based on separation and continuation of potential field. The new method is carried out in the following three steps. Firstly, potential feilds corresponding to strata of different depth on horizontal groud are gained through separating the potential fields on the plane by a cutting method. Secondly, the fields corresponding to strata of different depth on horizontal groud are reduced to a plane corresponding to the top surface of different depth strata by using downward continuation. Finally, according to the field on the top surface, inversion is conducted to get structure of apparent density or magnetization in frequency. The inversion technique characterized by faster computing speed, it does not need to divide the subsurround field sources region into many rectangular blocks in one time and does not need to slove linear algebraic equations as well. So, this technique can overcome the requirement of large computer memory, unstable solution and computation time bottleneck which hinders the application of 3Dinversion to practice.Several cases, including apparent density inversion of gravity anomolies in Xinjiang, Puguang gas field and the East China Sea and its adjacent area as well apparent magnetization inversion of magnetic anomaly in Huoqiu iron mine area, are presented to demonstrate the effect of applying this method. This method is suitable for 3D inversion of potential field in large area and has some theorical and practical significance. A visual software in Windows system is designed with Fortran language, C language, DLL technology and multithread technology based C++ Builder 6.0, which provides convenience for the use and popularization of new method.
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