Gravity inversion of a complex interface in the presence of interfering sources

We present a new semi-automatic gravity interpretation method for estimating a complex interface separating two media containing heterogeneities produced by the existence of interfering sources. The method combines a robust fitting procedure and the constraint that the interface is very smooth near the interfering sources whose approximate horizontal coordinates are defined by the user. The proposed method differs from the regionalresidual techniques by using no spectral content assumption about the interface to be estimated, i.e., the interface can produce a gravity response containing both low- and high-wavenumber features. As a result, it may be applied to map the relief of a complex interface in a geological setting containing either shallow- or deepseated interfering sources. Tests with synthetic data have shown that the method can be of utility in estimating the basement relief of a sedimentary basin in the presence of salt layers and domes or in the presence of mafic intrusions in the basement and/or in both basement and sediments. The method was applied to real gravity data from two geological setting having different kind of interfering sources and interface to be interpreted: 1) the anorthositie-tonalite interface over the outcrop East Bull gabbro anorthosite complex, Ontario, Canada; and 2) the sediments-basement interface over Algarve Basin, south Portugal. The results showed good agreement with the corresponding known geological features, even when the estimated interface and the interfering sources present highly overlapping spectral contents.