A FORTRAN-77 COMPUTER-PROGRAM FOR 3-DIMENSIONAL ANALYSIS OF GRAVITY-ANOMALIES WITH VARIABLE DENSITY CONTRAST

A computer program in FORTRAN 77 is presented to calculate the gravity anomalies of three-dimensional bodies with either a constant density contrast or linear decrease of density contrast with depth or a second order decrease of density contrast with depth. The decrease of density contrast in sedimentary basins may be approximated by a quadratic function. A sedimentary basin may be viewed as a number of prisms placed in juxtaposition. Approximate equations for prismatic bodies are developed for rapid calculation of gravity anomalies. Efficient methods are developed for three-dimensional analysis of gravity anomalies by an appropriate use of the exact and approximate equations. The depths to the basement are adjusted iteratively by comparing the calculated anomalies with the observed anomalies. Two field examples are given demonstrating the utility of the computer program.