The vertical flow in the lowermost mantle beneath the Pacific from inversion of seismic waveforms for anisotropic structure
The vertical flow in the lowermost mantle beneath the Pacific from inversion of seismic waveforms for anisotropic structure
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DOI：
10.1016/j.epsl.2010.05.037
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发表时间：
2010-08-15
影响因子：
5.3
通讯作者：
Geller, Robert J.
中科院分区：
文献类型：
--
作者：
Kawai, Kenji;Geller, Robert J.
利用走时数据直接约束横观各向同性（TI）介质的弹性常数是不切实际的。相反，正如我们在本文中所示，弹性常数可以直接确定体波波形数据的反演。我们反演的S和ScS阶段（以及任何其他阶段到达的时间窗口）的观测地震波形的水平分量，以确定在太平洋下地幔的TI剪切波速度的径向剖面。我们发现，径向（SV）分量是快于横向（SH）分量的深度范围内约200 - 400公里以上的核幔边界（CMB）。在该深度范围内，D "不连续面以上的主要矿物成分是镁钙钛矿（pv）和铁方镁石（fp）。观察到的各向异性可以解释为由于热浮力引起的垂直流动引起的最低地幔中pv、fp或两者的晶格优选取向（LPO），这可能与夏威夷热点的起源有关（尽管其他可能性，例如化学上不同的层）。不能排除后钙钛矿（ppv）的LPO或在化学致密堆中和周围逆流的LPO）。我们发现，SV剪切波的速度非常接近CMB的分辨率是固有的限制，由于零切向牵引力的边界条件在CMB剪切波分裂研究，因此不能用来调查最低地幔的各向异性。(C)2010 Elsevier B.V.保留所有权利。
It is impractical to directly constrain the elastic constants of a transversely isotropic (TI) medium using travel-time data. In contrast, as we show in this paper, the elastic constants can be determined straightforwardly by inversion of body-wave waveform data. We invert the horizontal components of observed seismic waveforms of S and ScS phases (as well as any other phases arriving in the time window) to determine the radial profile of TI shear wave velocity in the lowermost mantle beneath the Pacific. We find that the radial (SV) component is faster than the transverse (SH) component in the depth range from about 200-400 km above the core-mantle boundary (CMB). The major mineralogical components above the D" discontinuity in this depth range are Mg-perovskite (pv) and ferropericlase (fp). The observed anisotropy can be interpreted as due to lattice preferred orientation (LPO) of either pv, fp, or both in the lowermost mantle induced by vertical flow due to thermal buoyancy, which might be related to the origin of the Hawaiian hotspot (although other possibilities such as a chemically distinct layer. LPO of post-perovskite (ppv), or LPO in counter-flow in and around a chemically dense pile cannot be excluded). We show that resolution of the velocity of SV shear waves very close to the CMB is inherently limited due to the boundary condition of zero tangential traction at the CMB; shear wave splitting studies thus cannot be used to investigate the anisotropy of the lowermost mantle. (C) 2010 Elsevier B.V. All rights reserved.