A Comparative Study on Computing Horizontal Derivatives of Gravity Data for Geological Contact Mapping

Abstract

Computations of x- and y-components of the horizontal derivatives (gradients) from an anomaly grid (with  x- and y-axes directed east and north, respectively) still take an important place in potential field data-processing  techniques. These techniques may successfully bring out some significant subtle details that are masked in the  anomaly maps. Particularly abrupt lateral changes in densities and magnetizations effectively aid geological mapping  and these changes may be traced by some derivative-based techniques without specifying any prior information  about the nature of the potential field source bodies. Hence derivative-based techniques are regularly used in  the visual interpretation of potential field anomalies. It is well known that computation of horizontal derivatives  can be performed through either fast Fourier transform (i.e. in wave number domain) or simple finite-difference  equations (i.e. in space domain) to outline the geological source boundaries (edges). Numerous studies including  the use of either one have been recorded in the literature so far. In this study, comprehensive comparisons of the  solutions obtained from those techniques have been made using both synthetically produced and real gravity data  sets. Synthetic applications have been performed using both noise-free and noisy gravity data sets for two different  depth-to-source scenarios. Thus not only the signal-to-noise ratios but also the depth-to-source conditions have been  analyzed to test the performance of those approaches. Additionally, a real data experiment has been achieved using  regional Bouguer gravity anomalies from a portion of a well-known geological setting, the Aegean Graben System  (Western Anatolia, Turkey).