The removal of unwanted edge contours from gravity datasets
Gordon R. J. CooperSchool of Geosciences, University of the Witwatersrand, Johannesburg 2050, South Africa. Email: Gordon.Cooper@wits.ac.za
Exploration Geophysics 44(1) 42-47 https://doi.org/10.1071/EG12027
Submitted: 10 May 2012 Accepted: 12 September 2012 Published: 16 October 2012
Abstract
Gravity data is widely used in the search for mineral deposits, and can be collected using ground, borehole, airborne, shipborne and satellite platforms. The boundaries between rocks with differing densities result in boundaries in their corresponding gravity anomalies. These boundaries, or edges, can be located using techniques based on horizontal derivatives of the data. Edge contours that do not relate to the current interpretation project can be considered as noise, and high resolution data can possess a proliferation of such edges, making interpretation difficult. While smoothing can be applied to reduce the number of edges, it has the disadvantage that the remaining edge locations are shifted and the shape of the edge contours is altered. Three methods are discussed here for the removal of unwanted edge contours. The first method removes edges which are not present in the data after its upward continuation to a user-selected height. The second method removes edges whose amplitude is below a given threshold, and the final method removes the smallest edge contours.
Key words: potential fields, semi-automatic interpretation methods.
References
Beck, A. E., 1981, Physical principles of exploration methods: MacMillan Press.Blakely, R. J., and Simpson, R. W., 1986, Approximating edges of source bodies from magnetic and gravity anomalies: Geophysics, 51, 1494–1498
| Approximating edges of source bodies from magnetic and gravity anomalies:Crossref | GoogleScholarGoogle Scholar |
Boschetti, F., Hornby, P., and Horowitz, F. G., 2001, Wavelet based inversion of gravity data: Exploration Geophysics, 32, 48–55
| Wavelet based inversion of gravity data:Crossref | GoogleScholarGoogle Scholar |
Cella, F., Fedi, M., and Florio, G., 2009, Toward a full multiscale approach to interpret potential fields: Geophysical Prospecting, 57, 543–557
| Toward a full multiscale approach to interpret potential fields:Crossref | GoogleScholarGoogle Scholar |
Cooper, G. R. J., 2010, A modified tilt-depth method for Kimberlite exploration. 72nd EAGE Conference & Exhibition, 14–17 June 2010, Barcelona, Spain.
Cooper, G. R. J., and Cowan, D. R., 2009, Blocking borehole log data: Exploration Geophysics, 40, 233–236
| Blocking borehole log data:Crossref | GoogleScholarGoogle Scholar |
Cordell, L., and Grauch, V. J. S., 1985, Mapping basement magnetization zones from aeromagnetic data in the San Juan Basin, New Mexico, in W. J. Hinze, ed., The utility of regional gravity and magnetic anomaly maps: SEG, 181–197.
Eales, H. V., 2001, A first introduction to the geology of the Bushveld complex and those aspects of South African geology that relate to it: Council for Geoscience (Pretoria, South Africa).
Frimmel, H. E., Groves, D. I., Kirk, J., Ruiz, J., Chesley, J., and Minter, W. E. L., 2005, The formation and preservation of the Witwatersrand goldfields, the world’s largest gold province: Economic Geology, 100th anniversary volume, 769–797.
Jahne, B., 2005, Digital image processing (6th edition): Springer.
Mitasova, H., and Jarosalav, H., 1993, Interpolation by regularized spline with tension: II. Application to terrain modeling and surface geometry analysis: Mathematical Geology, 25, 657–669
| Interpolation by regularized spline with tension: II. Application to terrain modeling and surface geometry analysis:Crossref | GoogleScholarGoogle Scholar |
Reading, A., Bodin, T., Sambridge, M., Howe, S., and Roach, M., 2010, Down the borehole but outside the box: innovative approaches to wireline log data interpretation. ASEG-PESA Conference, August 2010, Sydney, Australia.
Sambridge, M., Bodin, T., Reading, A., and Gallagher, K., 2010, Inference from noisy data with an unknown number of discontinuities: ideas from outside the box. ASEG-PESA Conference, 1–4 August 2010, Sydney, Australia.
Telford, W. M., Geldart, L. P., and Sheriff, R. E., 1990, Applied geophysics (2nd edition): Cambridge University Press.