 Presentation options
The variable for the inversion is density contrast and the recovered model is shown on this page in two different ways. Recall that our objective function constructs smooth models, so discrete geological boundaries may appear as gradational changes, unless a particular value is used in the image, as in the iso-surface renderings. High density values are red, and low background values are red. Click the adjacent image for an animation of a series of slices through the model volume. Animations can help the viewer visualize volumetric information if display parameters are carefully chosen. This animation shows a series of horizontal slices moving from surface to 550 metres depth, and is approximately 98 kbytes in size.
Inversion constructs 3D models of density contrast, so interpretation requires an appropriate display for studying the resulting structures. A 3D cube of densities can be displayed in sectional or planar cuts or as a 3D image after volume rendering. Sectional cuts have the advantage that values of the physical property in each cell are displayed. These are the numbers which reproduce the field data. Above is an example of a plan-sectional cut made at a depth of 200 metres .
One disadvantage of the sectional cuts is that it is sometimes difficult to get a sense of 3D structure. This is where 3D volume rendered images have an advantage. But care must be taken, since a different threshold for volume rendering will generate a different image. The next figure illustrates two iso-surfaces with the lower density (outside) surface rendered as semi-transparent.
Comparison with drilling results
The figure below is a geological cross-section derived from drilling. The mineralized zone's outline corresponds approximately with the recovered model's 0.5 g/cc density-contrast isosurface. The overburden thickness inferred from the recovered model is slightly greater than the true value. Note that northing and easting coordinates used for inversion do not correspond to coordinates on the geology cross section.
| © UBC-GIF
January 9, 2007
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