Useful earth-science data occur in the form of orientations of lines that constitute an orientation distribution. Examples include fault trends, paleocurrent directions, and wind directions. Orientation data introduce some new challenges for presentation and for characterisation by statistics. Like constant-sum data, discussed in Chapter 7, they do not have an infinite range. Worse, the range is circular (0° to 360°, or 0 to 2π) so that the concept of an outlier, or a large variance, must be viewed cautiously. The most complete account of circular-orientation data is by Fisher (1993) although the concepts seem to have been first introduced formally into earth sciences by Cheeney (1983) and Till (1974), from the specialist monograph by Mardia (1972), subsequently expanded by Mardia and Jupp (2000).
KeywordsClay Anisotropy Sandstone Shale Magnetite
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