Derivative-based techniques for geological contact mapping from gravity data

Abstract

Gravity anomalies illuminate subsurface lithology and geological structure in three dimensions, which is vital for studies of concealed faults, sedimentary basins, basement lithology, and other geological targets. Although not all geological contacts correspond to lithological contacts, the contact mapping provides key information on structural regimes, deformation styles and trends. Many techniques for contact mapping have been developed. Here, we evaluate five methods applied to gridded data. The first two are the horizontal gradient magnitude of the gravity field (GF hgm), and tilt (TI hgm). The third and fourth rely on locating maxima of the analytic signal (AS) and the 3D local wavenumber (LW). The fifth is normalized standard deviation (NSTD) method. In this article, we evaluate the use of these five methods for mapping contacts and compare the results. First, synthetic vertically-sided models are used to quantify the offsets of maxima from the true contact location due to the source effects of finite source thickness, central depth, and width. Second, the effects of contact dip are discussed. Finally, a real data set is used to evaluate the ability of each method to produce maps of coherent contact trends in the presence of noise and gridding artifacts.