Direct measurements of spatially distributed vertical strain within ice masses are scientifically valuable but challenging to acquire. We use manual marker tracking and automatic cross correlation between two repeat optical televiewer (OPTV) images of an ~100 m-long borehole at Derwael Ice Rise (DIR), Antarctica, to reconstruct discretised, vertical strain rate and velocity at millimetre resolution. The resulting profiles decay with depth, from −0.07 a−1 at the surface to ~−0.002 a−1 towards the base in strain and from −1.3 m a−1 at the surface to ~−0.5 m a−1 towards the base in velocity. Both profiles also show substantial local variability. Three coffee-can markers installed at different depths into adjacent boreholes record consistent strain rates and velocities, although averaged over longer depth ranges and subject to greater uncertainty. Measured strain-rate profiles generally compare closely with output from a 2-D ice-flow model, while the former additionally reveal substantial high-resolution variability. We conclude that repeat OPTV borehole logging represents an effective means of measuring distributed vertical strain at millimetre scale, revealing high-resolution variability along the uppermost ~100 m of DIR, Antarctica.

中文翻译：

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通过光学望远镜重复钻孔测井获得的高分辨率分布式垂直应变和速度：Derwael Ice Rise，南极洲

直接测量冰块内空间分布的垂直应变具有科学价值，但难以获得。我们在南极洲德瓦尔冰隆 (DIR) 的一个约 100 米长的钻孔的两个重复光学电视 (OPTV) 图像之间使用手动标记跟踪和自动互相关，以毫米分辨率重建离散的垂直应变率和速度。生成的剖面随深度衰减，从 -0.07 a-1在表面到 ~-0.002 a-1从-1.3 ma到应变的基部-1在表面至 ~-0.5 ma-1以速度向基部。两个剖面也显示出很大的局部变异性。安装在相邻钻孔中不同深度的三个咖啡罐标记记录了一致的应变率和速度，尽管在更长的深度范围内取平均值并受到更大的不确定性。测得的应变率曲线通常与二维冰流模型的输出非常接近，而前者还显示出大量的高分辨率可变性。我们得出结论，重复 OPTV 钻孔测井是测量毫米级分布垂直应变的有效手段，揭示了南极洲 DIR 最高约 100 m 的高分辨率变化。