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Date: Tue, 23 Nov 1999 14:39:10 -0800
To: [log in to unmask]
From: Gerhard Oertel <[log in to unmask]>
Subject: Orientation of natural fractures
A colleague forwarded your request to me, I am not, and do not
plan to be, a subscriber to the geo-tectonics list. You can reach me
at: <[log in to unmask]>
Although K.V. Mardia's, Statistics of Directional Data, Academic
Press, London and New York, 1972, has been around for a while, his
Chapter 8, Distributions on Spheres, pp. 212-248, still seems to me
the most useful. Which model you want to choose for the
distribution of your observation points (fracture poles) may depend
on whether they form a single maximum or a girdle and on whether
their array seems to have a reasonably axial symmetry or not.
Not mentioned in Mardia's book is: Kamb, W.B., Ice petrofabric
observations from Blue Glacier, Washington, in relation to theory and
experiment. 1959, Jour. Geophys. Res., v.64, 1891-1909. Kamb's
writing style is not the easiest. His statistical approach to
contouring is strictly valid only for a distribution with a single
maximum, although I have seen it used where this was definitely not
the case.
How wide the solid angle with one standard deviation is, should
depend on both the total number of your measurements and on how
tightly they are clustered; no fixed number of degrees can be
applicable to all cases.
Perhaps this helps you.
Gerhard Oertel.
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John Whalley
Lecturer in Structural Geology and Computer Applications in Geology
List owner - geo-tectonics
Tel +44 23 9284 2247 Fax +44 23 9284 2244
School of Earth, Environmental and Physical Science
University of Portsmouth
Portsmouth, PO1 3QL, UK Email- [log in to unmask]
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