Modeling Magnetic and Gravity Anomalies
For a uniformly magnetized body, the magnetic anomaly can be computed using a surface integration method because there is no volumetric magnetization. However, for a strongly magnetized body if the surface of the body is not a quadratic surface, the magnetization inside the body is no longer uniform and volumetric magnetization exists. Thus, surface integration alone will not accurately calculate the magnetic anomaly. In this case, one can use numerical methods to solve the governing partial differential equation to compute the anomaly. The BEM is one of several methods that can be used.
In a space free of electrical currents, the magnetic field H and the magnetic induction intensity B satisfy
Figures & Tables
The boundary element method (BEM) divides only the boundaries of the region under investigation into elements, so it diminishes the dimensionality of the problem, e.g., the 3D problem becomes a 2D problem, and the 2D problem becomes a 1D problem. This simplifies inputting the model into a computer and greatly reduces the number of algebraic equations. The advantage of this is even more evident for some 3D and infinite regional problems that often are encountered in geophysics. Originally published in China, this well-organized book is likely the most comprehensive work on the subject of solving applied geophysical problems. Basic mathematical principles are introduced in Chapter 1, followed by a general yet thorough discussion of the BEM in Chapter 2. Chapters 3 through 7 introduce the applications of BEM to solve problems of potential-field continuation and transformation, gravity and magnetic anomalies modeling, electric resistivity and induced polarization field modeling, magnetotelluric modeling, and various seismic modeling problems. Finally, in Chapter 8, a brief discussion is provided on how to incorporate the BEM and the finite-element method (FEM) together. In each chapter, detailed practical examples are given, and comparisons to both analytic and other numerical solutions are presented. This is an excellent book for numerically oriented geophysicists and for use as a textbook in numerical-analysis classes.