PAGEOPH, Vol. 140, No. 3(1993)
Three-dimensional Analysis of Gravity Anomalies
of Sedimentary Basins by Polygonal Prismatic
Model with a Quadratic Density Function
D. Bhaskara Rao and N. Ramesh Babu
Abstract
The decrease of density contrast in sedimentary strata may be approximated by a
quadratic function. A sedimentary basin may be considered as a number of horizontal
polygonal prisms of finite thickness placed one over the other. Equations for the
gravity anomaly of an n-sided polygon prism have been derived using a quadratic
density function. A method has been developed for inversion of gravity anomalies
using a polygonal prismatic model. An analytical method has been employed for
evaluating the necessary derivatives as the computing time by this method is much
slower than by a numerical method. Approximate equations have been derived for
rapid calculation of the anomalies and derivatives. Efficient computer programs have
been developed for calculation of the anomalies and derivatives by an appropriate use
of the exact and approximate equations. The depth to the polygon prisms constituting
the basin are iteratively adjusted by minimizing the sum of the squares of the
differences between the observed and calculated anomalies. These methods have been
applied to analyze the Bouguer anomaly map of the Los Angeles basin, California.
Key words: Three-dimensional analysis, gravity anomalies, sedimentary basins,
polygonal prismatic model, quadratic density function, approximate equations.