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Earth and Space Sciences · 术语表

什么是 Orientation tensor?

Definition 8.5 University Earth and Space Sciences — Year 3 · 第 8 章 — Structural Analysis

The orientation tensor of NN unit vectors p⃗1,…,p⃗N\vec p_1, \dots, \vec p_N is the symmetric matrix

T=1N∑i=1Np⃗i p⃗iT,Tjk=1N∑ipij pik.T = \frac1N\sum_{i=1}^N \vec p_i\,\vec p_i^{\mathsf T}, \qquad T_{jk} = \frac1N\sum_i p_{ij}\,p_{ik} .

It does not change when a vector is replaced by its opposite, so it suits axes and poles, which have no sense. Its eigenvalues λ1≥λ2≥λ3≥0\lambda_1 \ge \lambda_2 \ge \lambda_3 \ge 0 add up to its trace, 11.

Pi-diagram of the Varden anticline on the equal-area net, lower hemisphere: the poles of twelve bedding readings (dots), the best-fit girdle from the orientation tensor (blue), the great circles of the two mean limbs (dashed) and the beta-axis (triangle), where all three great circles meet. A bed dipping east has its pole to the west of the centre.
Pi-diagram of the Varden anticline on the equal-area net, lower hemisphere: the poles of twelve bedding readings (dots), the best-fit girdle from the orientation tensor (blue), the great circles of the two mean limbs (dashed) and the beta-axis (triangle), where all three great circles meet. A bed dipping east has its pole to the west of the centre.
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