Mapping Crustal Shear Wave Velocity Structure and Radial Anisotropy Beneath West Antarctica Using Seismic Ambient Noise
Mapping Crustal Shear Wave Velocity Structure and Radial Anisotropy Beneath West Antarctica Using Seismic Ambient Noise
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DOI：
10.1029/2019gc008459
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发表时间：
2019-11
期刊：
影响因子：
3.7
通讯作者：
J. O’Donnell;A. Brisbourne;G. Stuart;C. Dunham;Y. Yang;G. Nield;P. Whitehouse;A. Nyblade;D. Wiens;S. Anandakrishnan;R. Aster;A. Huerta;A. Lloyd;T. Wilson;J. Winberry
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作者：
J. O’Donnell;A. Brisbourne;G. Stuart;C. Dunham;Y. Yang;G. Nield;P. Whitehouse;A. Nyblade;D. Wiens;S. Anandakrishnan;R. Aster;A. Huerta;A. Lloyd;T. Wilson;J. Winberry
使用从地震环境噪声中提取的8至25秒周期的瑞利波和洛夫波相速度频散数据，我们（i）模拟了西南极地壳的三维剪切波速度结构，（ii）绘制了地壳径向各向异性的变化。增强的区域分辨率由英国南极地震网络提供。在西南极裂谷系（WARS）中，一个从玛丽伯德地向南延伸的厚约26-30 km的地壳脊将罗斯海和阿蒙森海海湾中更延伸的地壳（厚约22 km）区域分开，这表明WARS新生代演化中的沿着走向变化。WARS的南部边缘被定义为沿着南部横贯南极山脉和哈格-埃尔斯沃思-惠特莫尔山脉（HEW）块体，地壳厚度梯度很大。在哈格冰原岛峰-埃尔斯沃思山脉下模拟了35-40 km厚的地壳，在惠特莫尔山脉下减少到30-32 km厚，反映了复合HEW块体内不同的结构域。我们的分析表明，下地壳和潜在的中地壳是积极的径向各向异性（VSH>VSV）在整个西南极洲。在HEW区块中观察到最强的各向异性特征，强调了其在西南极洲地壳单元中的独特来源，并且可以想象地反映了前寒武纪变质基底顶部的13 km厚的变质沉积物序列。WARS地壳中的正径向各向异性与拉伸环境中的观测结果一致，可能反映了拉伸变形导致的云母和角闪石等矿物的晶格择优取向。我们的观测结果支持了大陆地壳各向异性可能普遍存在的论点。
Using 8‐ to 25‐s‐period Rayleigh and Love wave phase velocity dispersion data extracted from seismic ambient noise, we (i) model the 3‐D shear wave velocity structure of the West Antarctic crust and (ii) map variations in crustal radial anisotropy. Enhanced regional resolution is offered by the UK Antarctic Seismic Network. In the West Antarctic Rift System (WARS), a ridge of crust ∼26–30 km thick extending south from Marie Byrd Land separates domains of more extended crust (∼22 km thick) in the Ross and Amundsen Sea Embayments, suggesting along‐strike variability in the Cenozoic evolution of the WARS. The southern margin of the WARS is defined along the southern Transantarctic Mountains and Haag‐Ellsworth Whitmore Mountains (HEW) block by a sharp crustal thickness gradient. Crust ∼35–40 km is modeled beneath the Haag Nunataks‐Ellsworth Mountains, decreasing to ∼30–32 km thick beneath the Whitmore Mountains, reflecting distinct structural domains within the composite HEW block. Our analysis suggests that the lower crust and potentially the middle crust is positively radially anisotropic (VSH>VSV) across West Antarctica. The strongest anisotropic signature is observed in the HEW block, emphasizing its unique provenance among West Antarctica's crustal units, and conceivably reflects a ∼13‐km‐thick metasedimentary succession atop Precambrian metamorphic basement. Positive radial anisotropy in the WARS crust is consistent with observations in extensional settings and likely reflects the lattice‐preferred orientation of minerals such as mica and amphibole by extensional deformation. Our observations support a contention that anisotropy may be ubiquitous in the continental crust.