Sonic methods for measuring crystal orientation fabric in ice, and results from the West Antarctic ice sheet (WAIS) Divide
Sonic methods for measuring crystal orientation fabric in ice, and results from the West Antarctic ice sheet (WAIS) Divide
复制标题
测量冰中晶体取向结构的声波方法以及西南极冰盖 (WAIS) 分水岭的结果
作者：
D. Kluskiewicz;E. Waddington;S. Anandakrishnan;D. Voigt;K. Matsuoka;M. McCarthy
摘要我们描述了在冰芯钻孔中用声波测量晶体取向组构的方法，特别注意在WAIS分水岭普遍存在的垂直环带组构。冰中垂直传播的压缩波的速度受冰晶c轴垂直聚集的影响。剪切波速度--特别是快剪切偏振和慢剪切偏振之间的速度分离--对方位各向异性敏感。WAIS Divide的声波数据补充了织物的薄片测量。薄的部分显示出稳定的过渡到强大的带状织物在上部2000米的冰，随后过渡到垂直杆织物低于2500米的深度。由于噪声以及该方法对环带结构固有的不敏感性，压缩波声波数据在上层冰中是不确定的。与现有的薄部分相比，声波数据提供了更好的分辨率的过渡到极点织物低于2500米，特别是包括垂直集群在3000米附近的突然增加。我们的压缩波测量解决了在几米的深度范围内发生的结构变化，这不能从可用的薄切片中推断出来，但只对天顶各向异性敏感。未来的测井仪器应设计成除了测量纵波外还测量横波，特别是在冰流模式有利于环带结构发育的地区进行测井。
ABSTRACT We describe methods for measuring crystal orientation fabric with sonic waves in an ice core borehole, with special attention paid to vertical-girdle fabrics that are prevalent at the WAIS Divide. The speed of vertically propagating compressional waves in ice is influenced by vertical clustering of the ice crystal c-axes. Shear-wave speeds – particularly the speed separation between fast and slow shear polarizations – are sensitive to azimuthal anisotropy. Sonic data from the WAIS Divide complement thin-section measurements of fabric. Thin sections show a steady transition to strong girdle fabrics in the upper 2000 m of ice, followed by a transition to vertical-pole fabrics below 2500 m depth. Compressional-wave sonic data are inconclusive in the upper ice, due to noise, as well as the method's inherent insensitivity to girdle fabrics. Compared with available thin sections, sonic data provide better resolution of the transition to pole fabrics below 2500 m, notably including an abrupt increase in vertical clustering near 3000 m. Our compressional-wave measurements resolve fabric changes occurring over depth ranges of a few meters that cannot be inferred from available thin sections, but are sensitive only to zenithal anisotropy. Future logging tools should be designed to measure shear waves in addition to compressional waves, especially for logging in regions where ice flow patterns favor the development of girdle fabrics.
影响因子：
5.2
作者：
H. Conway;L. A. Rasmussen
通讯作者：
H. Conway;L. A. Rasmussen