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

Abstract

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). Key Words: Fast Fourier transform, Finite-differences, First-order horizontal derivatives, Geological contact mapping, Gravity anomalies. Öz: Potansiyel alan verilerinin işlenmesinde belirti gridinden (x-ve y-eksenleri doğu ve kuzey yönelimli olacak şekilde) yatay türevlerin x-ve y-bileşenlerinin hesaplanması günümüzde de önemli bir yer tutar. Bu işlemlerle belirti haritalarında ilk bakışta gözlenemeyen önemli detaylar belirlenebilir. En önemlisi ise yoğunluk ve manyetizasyondaki