Strongly Depth-Dependent Ice Fabric in a Fast-Flowing Antarctic Ice Stream Revealed With Icequake Observations
Strongly Depth-Dependent Ice Fabric in a Fast-Flowing Antarctic Ice Stream Revealed With Icequake Observations
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冰震观测揭示了快速流动的南极冰流中与深度密切相关的冰结构
DOI：
10.1029/2022jf006853
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发表时间：
2023
期刊：
影响因子：
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通讯作者：
Kufner S
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文献类型：
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作者：
Kufner S
冰川冰的晶体取向结构影响其强度和流动。因此，在模拟冰流时，晶体结构是一个重要的考虑因素。在这里，我们表明，剪切波分裂（SWS）与冰川微震测量可以用来反演地震各向异性和冰组构，如果在统计意义上表示。拉特福德冰流（Rutford Ice Stream，RIS）是一个快速流动的南极冰流，是为大规模冰盖模型提供信息的关键环境。我们提供了来自冰川微震活动的> 200，000个SWS测量结果，这些测量结果在位于接地线上游1040公里处的38个地震站网络中进行了登记。这些数据的一个代表性的子集被倒置的冰结构。由于SWS的特点，它积累沿着射线路径，我们包括从雷达测量的深度结构的信息。我们发现以下三层结构与数据拟合最好：RIS底部附近的宽垂直锥形组构（500 m厚），中间垂直于水流方向的厚垂直环带组构（1，200 m厚），以及最上部400 m的倾斜锥形组构。这种结构的变化意味着冰的深度依赖性强度分布，中间层沿沿着流比跨流更难变形3.5倍。同时，中间层对剪切比对沿沿着流动的压缩或拉伸软16倍。如果这样的配置是代表快速流动的冰流，它将需要一个更复杂的冰盖模型中的粘度积分。
The crystal orientation fabric of glacier ice impacts its strength and flow. Crystal fabric is therefore an important consideration when modeling ice flow. Here, we show that shear‐wave splitting (SWS) measured with glacial microseismicity can be used to invert seismic anisotropy and ice fabric, if represented in a statistical sense. Rutford Ice Stream (RIS) is a fast‐flowing Antarctic ice stream, a setting crucial for informing large‐scale ice sheet models. We present >200,000 SWS measurements from glacial microseismicity, registered at a 38‐station seismic network located ∼40 km upstream of the grounding line. A representative subset of these data is inverted for ice fabric. Due to the character of SWS, which accumulates along the raypath, we include information on the depth structure from radar measurements. We find that the following three‐layer configuration fits the data best: a broad vertical cone fabric near the base of RIS (500 m thick), a thick vertical girdle fabric, orientated perpendicular to flow, in the middle (1,200 m thick), and a tilted cone fabric in the uppermost 400 m. Such a variation of fabric implies a depth‐dependent strength profile of the ice with the middle layer being ∼3.5 times harder to deform along flow than across flow. At the same time, the middle layer is a factor ∼16 softer to shear than to compression or extension along flow. If such a configuration is representative for fast‐flowing ice streams, it would call for a more complex integration of viscosity in ice sheet models.