Application Study On Power Spectrum Method For Estimating Depth Of Magnetic Source

In the interpretation of magnetic anomalies,information about depth of the magnetic source bodies tends to be very important, which is critical to geophysical and geological interpretation. Moreover, it is also useful in the estimation of depth to the bottom of sedimentary basins and to estimate depth of a magnetic ore body. This paper studied power spectrum method for average top-depth determination of magnetic source based on total magnetic anomaly.The application of the method of power spectrum in dealing with the magnetic data can date back to the 1960s and has its own particular characteristics in processing the data of magnetic anomalies in frequency domain. The most significant advantage of this method is that the convolution relation in space domain converts into product relation in frequency domain. Therefore, the spectrum of the magnetic anomalies is made up by the product relations of several independent factors, one of which is known as the depth factor that is only decided by the depth of the magnetic bodies.In 1966, Bhattacharyya gave the power spectrum expression of the total magnetic field intensity of single uniform magnetic rectangular prism for the first time, and put forward the moment spectrum method to directly calculate the depth of the interface of the magnetic body. On the basis of his theory, A.Spector and F.S.Grant proposed their method,which was based on the statistical theory to estimate the average depth of many geological units.As the vertical rectangular prism can be used to simulate different underground geological bodies and has been widely applied, the vertical rectangular prism is also used as forward model in this paper. In this paper, the field values of models with different heights, widths and deepening are put forward. Through the tests of the theoretical models, the conditions and issues that should be paid attention to in using the power spectrum method to estimate the depth of the magnetic source are summed up in the paper.Based on this theoretical foundation, Visual Basic and Fortran mixed programming are applied to obtain the objective of using the power spectrum method to estimate the depth of the magnetic source. Finally, the aeromagnetic data of the Qiangtang Basin of Qinghai-Tibet Plateau are processed by using this applied program.