GRAVITY INVERSION USING OPEN, REJECT, AND SHAPE-OF-ANOMALY FILL CRITERIA

A gravity inversion method is developed by iteratively applying open, reject, and fill (O-R-F) criteria within a model space comprising a great many rectangular prisms. Each prism is assigned a density contrast. The modeling procedure consists of filling some prisms while leaving others empty. Only one element is filled for each pass. Generally, elements are added only to the periphery of the growing model. Models can be allowed to grow in any combination of directions, or in all directions. By application of a shape-of-anomaly fill criterion, the model rapidly attains a form which yields gravity approximating the given gravity scaled down by some constant factor. As the model continues to grow, this scale factor approaches unity. The method readily yields inverse models comprising several thousand individual prisms. Examples presented here give applications to 2-D problems. The method is readily applicable to 212-D and 3-D problems as well. Overhanging elements are obtained by appropriate use of model constraints. Initial density models are not required but they are allowed. An expanding seed method is explained which efficiently generates sets of inverse models by using dense models to initiate development of less dense models. The method is applied to inversion of several synthetic gravity profiles from known density models. A density model is also derived from gravity across the Troodos massif in Cyprus. Using a density contrast of 310kg/m3, the resultant model extends from the surface to a depth of 20.6 km and has a center of mass distribution displaced approximately 7 km to the northeast of the anomaly peak. © 1986 Society of Exploration Geophysicists.