Inversion of gravity data using a binary formulation

We present a binary inversion algorithm for inverting gravity data in salt imaging. The density contrast is restricted to being one of two possibilities: either zero or one, where one represents the value expected at a given depth. The algorithm is designed to easily incorporate known density contrast information, and to overcome difficulties in salt imaging associated with nil zones. The problem of salt imaging may be formulated as a general inverse problem in which a piecewise constant density contrast is constructed as an indirect means of identifying the salt boundary. Difficulty arises when the salt body crosses the nil zone in depth. As a result, part of the salt structure is invisible to the surface data and many inversion algorithms have difficulties in recovering the salt structure correctly. The binary condition places a strong restriction on the admissible models so that the non-uniqueness caused by nil zones might be resolved. In this paper, we will present the binary formulation for inversion of gravity data, develop the solution strategy, illustrate it with numerical examples, and discuss limitations of the technique.