Panning Mark, Romanowicz Barbara
Berkeley Seismological Laboratory, 215 McCone Hall, University of California, Berkeley, CA 94720, USA.
Science. 2004 Jan 16;303(5656):351-3. doi: 10.1126/science.1091524.
We applied global waveform tomography to model radial anisotropy in the whole mantle. We found that in the last few hundred kilometers near the core-mantle boundary, horizontally polarized S-wave velocities (VSH) are, on average, faster (by approximately 1%) than vertically polarized S-wave velocities (VSV), suggesting a large-scale predominance of horizontal shear. This confirms that the D" region at the base of the mantle is also a mechanical boundary layer for mantle convection. A notable exception to this average signature can be found at the base of the two broad low-velocity regions under the Pacific Ocean and under Africa, often referred to as "superplumes," where the anisotropic pattern indicates the onset of vertical flow.
我们应用全球波形层析成像技术来模拟整个地幔中的径向各向异性。我们发现，在地核-地幔边界附近的最后几百公里处，水平偏振的S波速度（VSH）平均比垂直偏振的S波速度（VSV）快（约1%），这表明水平剪切在大尺度上占主导地位。这证实了地幔底部的D"区域也是地幔对流的一个力学边界层。在太平洋和非洲下方两个广阔的低速区域底部可以发现一个明显的例外，这两个区域通常被称为“超级地幔柱”，在那里各向异性模式表明垂直流的开始。
