Forward gravity modeling of basement interfaces implies calculating the theoretical response of the geometry of the problem. The sedimentary fill above the basement interface is approximated by an ensemble of 3-D vertical prisms, one placed below each of the observation points. The width and strike length of each of the prisms is made equal to the station spacing and profile interval, respectively. The theoretical gravity anomaly at any point on the XY plane is obtained by computing the algebraic sum of the gravity effects of the prisms. The decrease of density contrast in sedimentary basins may be approximated by a simple mathematical function for example quadratic density function which was used here. Equations in closed form for the gravity anomalies of 3D prismatic models are derived. Juxtaposed 3-D rectangular/square blocks with their geometrical epicenters on top coincide with grid nodes of a mesh to approximate a sedimentary basin. Efficient methods and a MATLAB program, GRAV3DMOD have been developed for anomaly calculation by solving the equations. We demonstrate the validity of this program by computing the theoretical gravity response of the Los Angeles basin, California by making use of the available basement relief contour map of the basin (Chai and Hinze, 1988).


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