A 3-D gravity inversion tool based on exploration of model possibilities

Abstract

A computational tool for the development and implementation of a recently published method of 3-D (three dimensional) inversion for gravity data is presented. This method seeks to determine the geometry of an indefinite number of anomalous bodies with prescribed (fixed or variable) density contrasts, positive and negative values being indiscriminately accepted in the model. The approach is based on a prismatic partition of the subsurface and attempts to determine the anomalous bodies by means of a “growth” sequence, analysing (systematically or randomly) the several model possibilities and from that choosing the best for the growth progress. Moreover, a regional trend for the gravity data can be simultaneously adjusted. The non-uniqueness of the gravity inversion is avoided by means of a mixed condition about the residuals and the whole body anomalous mass. This inversion method has been applied with good results to simulation tests and to several real examples. Here, we present a main program that realises the inversion according to several possibilities for general application (scale of the survey, fixed or variable density contrasts, optional smoothing, optional trend adjustment, systematic or random exploration, optional a priori information, weighting, etc.). This program is presented along with a previous program for selection of unknowns and parameters and another program for visual presentation of the results. All three programs are written in Fortran 77 and completes the inversion tool.