A Note on the Use of the Second Vertical Derivative (SVD) of Gravity Data with Reference to Indonesian Cases
Keywords:anomaly enhancement, basin delineation, fault, gradient, potential field
AbstractGravity data analysis and interpretation are based, among others, on their spatial variation represented by horizontal and vertical gradients. The gradient or derivative of a gravity field can be calculated either in the spatial domain or the wave-number domain. Historically, the second vertical derivative (SVD) of gravity data can be used to delineate the boundaries of anomalous sources. This paper addresses inappropriate use of the SVD of gravity data, with reference to current practices in Indonesia. The SVD's relative magnitude along a profile is widely used to define whether a density contrast and its dipping orientation correspond to a normal or reverse fault, which may be geologically incorrect. Furthermore, the SVD is calculated by approximation using the horizontal derivative, which may be erroneous especially with poorly distributed data and anomalous 3D sources. We exemplify our analysis with synthetic data and propose a more appropriate spectral-based analysis using field data.
LaFehr, T.R. & Nabighian, M.N., Fundamentals of Gravity Exploration, Geophysical Monograph Series 17, SEG, 2012.
Fairhead, J.D., Advances in Gravity and Magnetic Processing and Inter-pretation, EAGE Publications, 2015.
Roy, L., Agarwal, B.N.P. & Shaw, R.K., A New Concept in Euler Deconvolution of Isolated Gravity Anomalies, Geophysical Prospecting, 48(3), pp. 559-575, 2000.
Ma, G., Combination of Horizontal Gradient Ratio and Euler Methods for the Interpretation of Potential Field Data, Geophysics, 78(5), pp. J53-J60, 2013.
Blakely, R.J., Potential Theory in Gravity and Magnetic Applications, Cambridge University Press, 1996.
Elkins, T.A., The Second Derivative Method of Gravity Interpretation, Geophysics, 16(1), pp. 29-50, 1951.
Baranov, V., Potential Fields and their Transformations in Applied Geo-physics, Geoexploration Monograph 6, Geopublication Associates, 1975.
Widianto, E., Determination of Basement Structure Configuration and Basin Types Using Gravity Data and its Implication for Oil and Gas Exploration Target in Java, Doctoral thesis, Institut Teknologi Bandung, 2008. (Text in Indonesian with English abstract)
Sarkowi, M., Identification of Structures in Ulubelu Geothermal Field Based on SVD Data Analysis of Bouguer Anomaly (in Indonesian with English abstract), Jurnal Sains MIPA, 16(2), pp. 111-118, 2010.
Hartati, A., Identification of Fault Structure Based on Derivative Analysis of Gravity in Celebes Island, Undergraduate Final Project, Universitas Indonesia, 2012. (Text in Indonesian with English abstract)
Ali, Y.H., Azimi, A. & Wulandari, A., Mapping of Nusa Laut Fault Based on Nusa Laut August-September 2015 Earthquake Hypocenters and Gravity Data, Proceedings of National Seminar on Physics and its Applications, Universitas Padjadjaran, pp. FB11-FB18, 2015. (Text in Indonesian with English abstract)
Mickus, K.L. & Hinojosa, J.H., The Complete Gravity Gradient Tensor derived from the Vertical Component of Gravity: A Fourier Transform Technique, Journal of Applied Geophysics, 46(3), pp. 156-176, 2001.
Grandis, H. & Dahrin, D., Full Tensor Gradient of Simulated Gravity Data for Prospect Scale Delineation, Journal of Mathematics and Funda-mental Sciences, 46, pp. 107-124, 2014.
Grandis, H. & Dahrin, D., The Utility of Free Software for Gravity and Magnetic Advanced Data Processing, IOP Conf. Series: Earth and Environmental Science, 62(012046), 2017.
Bott, M.P.H., A Simple Criterion for Interpreting Negative Gravity Ano-malies, Geophysics, 27(3), pp. 376-381, 1962.
Reynolds, J.M., An Introduction to Applied and Environmental Geophy-sics, 2nd Edition, Wiley-Blackwell, 2011.
Li, Y. & Oldenburg, D.W., 3D Inversion of Gravity Data, Geophysics, 63(1), pp. 109-119, 1998.
Spooner, A.M., Geology for Dummies, John Wiley & Son, 2011.
Untung, M. & Sato, Y., Gravity and Geological Studies in Jawa, Indonesia, Geological Survey of Indonesia & Geological Survey of Japan, 1978.
Buttkus, B., Spectral Analysis and Filter Theory in Applied Geophysics, Springer, 2000.
Sanchez-Rojas, J., New Bouguer Gravity Maps of Venezuela: Representa-tion and Analysis of Free-Air and Bouguer Anomalies with Emphasis on Spectral Analyses and Elastic Thickness, International Journal of Geo-physics, Article ID 731545, 2012.