The determination of true orientations of fractures in rock cores

Abstract

Determination of the true orientations of fractures in diamond drill cores obtained from deep boreholes in plutonic bodies is an essential requirement of the geoscience component of the Canadian Nuclear Fuel Waste Management Program. A reference line can be painted on the entire length of the rock core, indicating the orientation of the core, and the apparent orientation of the fracture can be measured from this reference line. This paper describes three methods that have been developed to convert the apparent orientation to true orientation, namely, stereographic projection, spherical trigonometry, and analytical geometry. The results obtained from these techniques were compared to assess their relative accuracy. Whereas the graphical method is more readily adaptable for use in the field, the mathematical methods can be computer-programmed and the programs GEOCORE and ORIENTC are available from the Geological Survey of Canada to facilitate the calculation of large volumes of data. Keywords: true orientation, fracture, rock core, stereographic projection, spherical trigonometry, analytical geometry.