Inferences of viscosity from the oceanic geoid: Indication of a low viscosity zone below the 660-km discontinuity
Inferences of viscosity from the oceanic geoid: Indication of a low viscosity zone below the 660-km discontinuity
复制标题
从海洋大地水准面推断粘度：表明 660 公里间断面以下存在低粘度区域
DOI：
10.1016/s0012-821x(97)81843-2
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发表时间：
1997
影响因子：
5.3
通讯作者：
O. Čadek
中科院分区：
文献类型：
--
作者：
M. Kido;O. Čadek
我们试图从海洋下面的大地水准面和层析结构中推断出地幔顶部1000公里处的粘性结构的细节。为了消除俯冲带和大陆下方有问题的质量体的重力信号，我们只考虑了海洋大地水准面的中间度（δ = 12-25）。遗传算法已被用来确定家庭的粘度模型，提供最好的相关性与观测大地水准面。我们的反演清楚地确定了岩石圈下面的软流圈，也证实了先前的推断预测的下地幔的粘度增加，但表明主要的粘度跳跃发生在约1000公里的深度，而不是在通常所说的660公里的边界。在400-1000 km深度范围内的某个地方，可能存在低粘度区，其粘度降低到与软流圈相当的值。这种低粘度区的存在是支持最近的深地幔各向异性的分析，有利于在下地幔的顶部具有较强的水平分量的流动模式。不幸的是，反演的分辨率以及最近的地震层析成像模型的质量不足以定位深度，并且不足以为该低粘度通道的粘度提供更高的精度。
We have attempted to infer details of the viscosity structure in the top 1000 km of the mantle from the geoid and tomographic structure beneath the oceans. In order to eliminate the gravity signal from problematic masses located below the subduction zones and the continents, we have considered only the intermediate degrees of the oceanic geoid (ℓ = 12–25). A genetic algorithm has been used to determine the family of viscosity models which give the best correlation with the observed geoid. Our inversion clearly identifies the asthenosphere just below the lithosphere and also confirms the viscosity increase in the lower mantle predicted by previous inferences, but suggests that the main viscosity jump occurs at a depth of about 1000 km and not at the usually stated 660-km boundary. Somewhere in the depth range of 400–1000 km, a low viscosity zone may exist where the viscosity decreases to a value comparable with the asthenosphere. Existence of such a low viscosity zone is supported by recent analysis of deep mantle anisotropy which favours a flow pattern with a strong horizontal component in the top part of the lower mantle. Unfortunately, the resolution of the inversion as well as the quality of recent seismic tomographic models are not sufficient to localize the depth and to come up with a higher accuracy for the viscosity of this low viscosity channel.