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Earth and Space Sciences · 术语表

什么是 Mean orientation (vector mean)?

又称: mean orientation

Definition 6.4 University Earth and Space Sciences — Year 1 · 第 6 章 — Field and Lab Methods I

For a plane of dip direction α\alpha and dip δ\delta, let

n⃗=(sin⁡δsin⁡α, sin⁡δcos⁡α, cos⁡δ)\vec n = (\sin\delta\sin\alpha,\ \sin\delta\cos\alpha,\ \cos\delta)

be its upward unit normal in east, north and up components. The mean orientation (or vector mean) of NN readings of normals n⃗1,…,n⃗N\vec n_1, \dots, \vec n_N is the plane whose normal is m⃗=S⃗/∥S⃗∥\vec m = \vec S/\|\vec S\|, where S⃗=∑in⃗i\vec S = \sum_i \vec n_i is their resultant; Rˉ=∥S⃗∥/N\bar R = \|\vec S\|/N is the mean resultant length. The mean dip direction and dip are αˉ=atan2⁡(SE,SN)\bar\alpha = \operatorname{atan2}(S_E, S_N) and δˉ=arccos⁡(SU/∥S⃗∥)\bar\delta = \arccos(S_U/\|\vec S\|).

Twenty-five simulated readings of the bedding of the Varden east limb, whose model attitude is 080.7/12.2, each with errors of 3 standard deviation on both angles, rounded to the degree. Solid line: the mean; dashed: one standard deviation either side (080.8 ± 2.9 and 12.4 ± 2.1). The vector mean of the 25 readings is 080.9/12.3.
Twenty-five simulated readings of the bedding of the Varden east limb, whose model attitude is 080.7/12.2080.7/12.2, each with errors of 3∘3{}^{\circ} standard deviation on both angles, rounded to the degree. Solid line: the mean; dashed: one standard deviation either side (080.8±2.9080.8 \pm 2.9 and 12.4±2.112.4 \pm 2.1). The vector mean of the 25 readings is 080.9/12.3080.9/12.3.
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