Compressional and shear wave velocities in South Island, New Zealand rocks and their application to the interpretation of seismological models of the New Zealand crust
Compressional and shear wave velocities in South Island, New Zealand rocks and their application to the interpretation of seismological models of the New Zealand crust
复制标题
新西兰南岛岩石的压缩波和剪切波速度及其在新西兰地壳地震模型解释中的应用
DOI：
10.1029/175gm08
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
D. Okaya
中科院分区：
文献类型：
--
作者：
N. Christensen;D. Okaya
使用实验室速度测量结果研究了新西兰南岛一组变质岩和火成岩的地震特性，将其作为高达 1000 MPa 围压的函数。速度测量的代表性样本是从 Caples、Aspiring、Torlesse、Buller 和 Takaka Terranes 收集的。研究的岩性包括石英长岩片岩、角闪岩、绿片岩、板岩、泥岩、杂砂岩、辉长岩和花岗岩。一般来说，地震速度随着密度的增加而增加。全岩石地球化学分析表明速度随着SiO 2 含量的降低而增加。哈斯特片岩和 Torlesse 样品的压缩波速度随着镁含量的增加而增加，但哈斯特片岩的速度与变质程度没有任何相关性。由于优选的矿物取向，哈斯特片岩具有高度各向异性，而 Torlesse 杂砂岩则具有各向同性。各向异性岩石的对称性从轴向到正交，具有平行于线状的快速压缩波速度。剪切波分裂仅对于与叶理法线成大角度的传播方向才有意义；其他角度的最小产量可能会被错误地解释为各向同性介质造成的。在哈斯特片岩正交方向上进行的折射实验显示出 6% 的压缩波各向异性，与实验室测量结果非常吻合。我们得出的结论是，地震各向异性是南岛地壳大部分地区的普遍特征。
The seismic properties of a suite of metamorphic and igneous rocks from South Island, New Zealand have been investigated using laboratory velocity measurements as a function of confining pressures up to 1000 MPa. Representative samples for the velocity measurements were collected from the Caples, Aspiring, Torlesse, Buller, and Takaka Terranes. Lithologies studied include quartzofeldspathic schists, amphibolites, greenschists, slates, argillites, graywackes, gabbros and granites. Seismic velocities, in general, increase with increasing density. Whole rock geochemical analyses show velocities increase with decreasing SiO 2 contents. Compressional wave velocities increase with increasing Mg numbers for Haast Schist and Torlesse samples, however velocities of the Haast schist rocks do not show any correlation with metamorphic grade. Haast schists are highly anisotropic due to preferred mineral orientations, whereas the Torlesse greywackes are isotropic. Symmetry of the anisotropic rocks varies from axial to orthorhombic, with fast compressional wave velocities parallel to lineations. Shear wave splitting is only significant for propagation directions at high angles to foliation normals; minimal production at other angles can mistakenly be interpreted as due to isotropic media. A refraction experiment shot in orthogonal directions across the Haast Schist shows 6% compressional wave anisotropy, in good agreement with the laboratory measurements. We conclude that seismic anisotropy is a pervasive feature throughout much of the South Island crust.