A direct method for interpreting magnetic anomalies—the case of a horizontal circular cylinder

A new method is introduced here to interpret the magnetic anomalies with special reference to vertical magnetic anomalies of a horizontal circular cylinder. The parameters of the cylinder are found to be related toV, ∂V/∂x and∂V/∂z at the origin of the cylinder. HereV is the observed anomaly,∂V/∂x and∂V/∂z are its horizontal and vertical derivatives respectively. The origin may be located working out an equality,viz.,3(∂V/∂z) ²=2V∂²V/∂z² which is true only at the origin. Thus, once the cylinder is located,V, ∂V/∂x and∂V/∂z at its origin can be determined and hence its parameters. The procedure is illustrated with a theoretical example.     

Characteristic curves for interpreting gravity anomalies of vertical cylinders and horizontal circular discs

Characteristic curves for the complete interpretation of a wide range of parameters of a vertical cylinder and a horizontal circular disc are presented. It is established that the distance of the inflexion point on the gravity profile of a vertical cylinder from the point of maximum anomaly [i.e. the origin] is approximately equal to the radius of the vertical cylinder, thus enabling one to demarcate the boundary of the vertical cylinder directly from the contour map based on the cluster of contours. Two gravity profiles, one across an anomalous zone in central Alberta, Canada and the other over Borsad area, India are interpreted by the curves presented and the results are shown.     

Magnetic anomalies of two-dimensional bodies and algorithms for magnetic inversion of dykes and basement topographies

Generalized equations for the anomalies in any component of the earth’s magnetic field due to two-dimensional bodies of arbitrary magnetization are derived in terms of a new parameter, called the direction of measurement. Schemes for inverting the magnetic anomalies of arbitrarily magnetized dykes and basement topographies are then developed and the relevant computer software is presented. In both the schemes, the initial values of the parameters are calculated by the computer, so that the input merely consists of the anomalies and their distances. The differences in the observed and calculated anomalies are solved iteratively for the errors in initial values of the parameters.     

重磁对应分析方法在东北地区实际资料处理中的应用

本文从泊松定理出发,设计三度体理论模型,运用重磁对应分析方法,研究理论模型的重磁异常相关系数R、斜率B和截距A。由其等值线图得出点、线距的疏密不影响分析窗口半径的选择,确定了分析窗口半径的选择范围在模型半径的1.5倍左右以及截距的变化是剩磁反映的结论。进而从东北地区实际资料的重磁对应分析方法处理中推断出:该区强磁性岩石的剩磁较强,且由重磁异常的斜率B和截距A确定了强磁与剩磁的分布范围。