Time-lapse imaging of subglacial drainage conditions using three-dimensional inversion of borehole electrical resistivity data
Time-lapse imaging of subglacial drainage conditions using three-dimensional inversion of borehole electrical resistivity data
复制标题
DOI：
10.3189/172756506781828854
复制
发表时间：
2006
影响因子：
3.4
通讯作者：
B. Kulessa;B. Hubbard;Giles H. Brown
中科院分区：
文献类型：
--
作者：
B. Kulessa;B. Hubbard;Giles H. Brown
摘要：我们在瑞士阿罗拉上冰川钻的四个钻孔底部记录了电阻率数据。在融化季节末期的两个昼夜水文循环中，每小时重复采集一次数据，间隔 10 天。约束三维 (3-D) 数据反演允许重建冰下沉积物层体电阻率的每小时变化。反演电阻率模型反映了研究区在两个水文循环之间渠道化冰下排水的建立，与之前的工作一致。体积电阻率和水电阻率的每日变化是同相的，并且体积电阻率幅度随着远离冰下河道而减小。利用选定的电-水力关系，我们估计了冰下沉积物层的水力传导率和孔隙度的米级变化，考虑到随着距河道距离的增加，粘土含量增加，中值颗粒半径减小。计算得出水力传导率和孔隙度分别从河道处的(6.4±2.1)×10–2ms–1和0.34±0.01减少到距离河道5m处的(3.3±2.2)×10–2ms–1和0.26±0.01。水力传导率估计值与先前推断的值一致，并且孔隙率估计值落在未石化冰下沉积物的预期范围内。我们得出的结论是，重复 3D 冰下电阻率数据的收集和反演是可行的，并且能够生成冰下水力过程和特性的多维图像。
Abstract We recorded electrical resistivity data at the base of four boreholes drilled through Haut Glacier d’Arolla, Switzerland. The data were acquired repetitively every hour over two diurnal hydrological cycles in the late melt season, separated by 10 days. Constrained three-dimensional (3-D) data inversion allowed reconstruction of hourly variations in bulk resistivity in the subglacial sediment layer. Inverted resistivity models reflect the establishment of channelized subglacial drainage in the study area between the two hydrological cycles, in agreement with previous work. Daily variations in bulk and water resistivity are in phase, and bulk resistivity amplitudes decrease away from the subglacial channel. Using selected electrical–hydraulic relationships, we estimate metre-scale changes in the hydraulic conductivity and porosity of the subglacial sediment layer, accounting for increasing clay content and decreasing median grain radius with distance from the channel. Hydraulic conductivity and porosity were respectively calculated to decrease from (6.4 ± 2.1) × 10–2ms–1 and 0.34 ± 0.01 at the channel to (3.3 ± 2.2) × 10–2ms–1 and 0.26 ± 0.01 at a distance of 5m from it. The hydraulic conductivity estimates are in agreement with previously inferred values, and the porosity estimates fall within the expected range for unlithified subglacial sediments. We conclude that collection and inversion of repeat 3-D subglacial resistivity data is feasible and has the capacity to generate multidimensional images of subglacial hydraulic processes and properties.