Overview

The gravity method is commonly referred to as a potential field method because it involves measurements that are a function of the potential of the observed gravitational field of force of the Earth. “Potential” is defined by the amount of work done in moving a particle from one position to another in the presence of a force field acting upon the particle. Thus, potential is a function of force-field space such that its rate of change is the component of force in that direction, which is related to the acceleration of gravity measured in the gravity method. This concept leads to a number of fundamental laws and theorems, such as Laplace's and Poisson's equations, Gauss' law, and Poisson's theorem, which are useful in understanding the properties of the gravity field and its analysis. These results extend to an arbitrary distribution of source particles by summing at the observation point the potential effects of all the particles of the body.

Forward models with closed form analytical expressions involve idealized sources with simple symmetric shapes (e.g. spherical, cylindrical, prismatic) that can be volume-integrated in closed form at the observation point. Forward models without closed form expressions involve general sources with irregular shapes that must be numerically integrated by filling out the volumes with idealized sources and summing the idealized source effects at the observation point. The numerical integration can be carried out with least-squares accuracy by distributing idealized sources throughout the general source according to the Gauss-Legendre quadrature decomposition of the irregular volume. The gravity effects of all conceivable distributions of mass can be modeled to interpret the significance of gravity anomalies.