Three‐dimensional (3-D) interactive modeling permits integrated processing and interpretation of gravity and magnetic data, yielding an improved geologic interpretation. 3-D model bodies are constructed from polyhedra of suitable geometry and physical parameters (density and susceptibility), input on an interactive graphics terminal that is tied to a host computer. The method is especially designed for concurrent processing and interpretation in an interactive mode. The effect on gravity of a homogeneous polyhedron is calculated by transforming a volume integral into a sum of line integrals. Magnetic effects can be modeled by using either Poisson’s theorem or a slight modification of the formulas derived for gravity modeling. The interactive modeling program allows the user to change the geometry as well as the density and/or susceptibility of the elementary polyhedra and to observe results quickly during the course of processing. This capability enables the interpreter to decide immediately if and where a tentative geologic structure must be changed for the modeled effect to fit that of a field survey. He is able to drive the device‐dependent process by clear menu functions without any knowledge of the rather complicated data structure and the interaction between the main program and its many subroutines. In addition, application of this method requires considerably less computing time than conventional methods based on the direct evaluation of volume integrals.

Modern geophysical interpretation requires an interdisciplinary approach and software capable of handling multiple geophysical data types such as seismic, full tensor gravity gradiometry, magnetics and magnetotellurics. We use the IGMAS+ (Interactive Gravity and Magnetic Application System) geo‐modelling software that is designed for 3D gravity, gravity gradient and magnetic modelling. This paper deals with a special aspect of potential field modelling, combining conventional triangulated model geometries (building polyhedrons) with voxel cubes. The hybrid modelling combines the advantages of both the vector and raster modelling system: both may be used alone (polyhedrons without voxels, voxels without polyhedrons) or simultaneously by superposition of both effects, which provides flexibility towards full interoperability. The key idea of our approach is, on the one hand to use two different, completely independent geometries (vector and raster) and give on the other hand the possibility to link both on demand for either editing the voxel model or to combine a large number of voxel cells under a common physical parameter function – which results in more reliable parameter inversion results.

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From 1982 to 1986, more than 2500 gravity data were taken in an Andean Geotraverse covering northern Chile and northwestern Argentina between 64° and 71°W and 20° and 26°S. Including 2100 reprocessed older data, there is now a data base of about 4600 gravity values available, which can be used together with other geophysical and geologicalin formation for an interdisciplinary interpretation to solve some problems of the structure and development of the Central Andes. The new gravimetric data base, which includes the Bouguer‐, free‐air‐ and isostatic residual anomaly, is presented together with a preliminary interpretation.

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We would like to thank V. I. Starostenko for his interest in our paper and his historical remarks on the development of 3‐D modeling formulas in gravity and magnetics. The main objective of our paper was to publish a user‐friendly fast interpretation tool for 3‐D modeling including interactive computer graphics. Therefore, it does not deal with an extended derivation of the formulas used in potential field theory.