Pseudo 3‐D P wave refraction seismic monitoring of permafrost in steep unstable bedrock
Pseudo 3‐D P wave refraction seismic monitoring of permafrost in steep unstable bedrock
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DOI：
10.1002/2012jf002638
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发表时间：
2014-02
期刊：
影响因子：
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通讯作者：
M. Krautblatter;D. Draebing
中科院分区：
文献类型：
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作者：
M. Krautblatter;D. Draebing
在陡峭的岩壁中，退化的冻土会导致危险的岩石蠕变和岩石边坡破坏。在不稳定的尺度上运作的永久冻土退化的空间和时间模式是复杂的，而且人们对它的了解很少。首次将P波地震折射层析成像（SRT）应用于陡坡岩壁冻土退化监测。在瑞士Matter Valley的一个不稳定的陡峭的NE-SW向峰线上安装了一个2.5-D测量，其中有5个80 m长的平行样带。在实验室中，在20°C和−5°C之间对水饱和的低孔隙度副片麻岩样品的P波速度进行了校准，当冻结时，沿着沿着和垂直于解理的P波速度分别显著增加0.55-0.66 km/s（10-13%）和2.4-2.7 km/s（>100%）。因此，地震折射在技术上是可行的，可以探测构成陡峭岩壁的低孔隙度岩石中的永久冻土。射线密度高达100或更高，划定了未冻结和冻结基岩之间的边界，并有助于准确定位活动层。SRT显示每月（2006年8月和9月）和每年的活动层动态（2006年8月和2007年），并揭示了一个连续的多年冻土体以下的东北面的活动层深度从2到10米的年度变化。大的冰填充的裂缝，冰川的侧向冻结，和一个持续的雪檐导致以前未报告的永久冻土模式接近表面和沿着波峰线，对应于活跃的季节性岩石位移高达几毫米/年。SRT提供了一个几何高分辨率的地下监测活动层动态在陡峭的永久冻土岩石的规模不稳定。
Degrading permafrost in steep rock walls can cause hazardous rock creep and rock slope failure. Spatial and temporal patterns of permafrost degradation that operate at the scale of instability are complex and poorly understood. For the first time, we used P wave seismic refraction tomography (SRT) to monitor the degradation of permafrost in steep rock walls. A 2.5‐D survey with five 80 m long parallel transects was installed across an unstable steep NE‐SW facing crestline in the Matter Valley, Switzerland. P wave velocity was calibrated in the laboratory for water‐saturated low‐porosity paragneiss samples between 20°C and −5°C and increases significantly along and perpendicular to the cleavage by 0.55–0.66 km/s (10–13%) and 2.4–2.7 km/s (>100%), respectively, when freezing. Seismic refraction is, thus, technically feasible to detect permafrost in low‐porosity rocks that constitute steep rock walls. Ray densities up to 100 and more delimit the boundary between unfrozen and frozen bedrock and facilitate accurate active layer positioning. SRT shows monthly (August and September 2006) and annual active layer dynamics (August 2006 and 2007) and reveals a contiguous permafrost body below the NE face with annual changes of active layer depth from 2 to 10 m. Large ice‐filled fractures, lateral onfreezing of glacierets, and a persistent snow cornice cause previously unreported permafrost patterns close to the surface and along the crestline which correspond to active seasonal rock displacements up to several mm/a. SRT provides a geometrically highly resolved subsurface monitoring of active layer dynamics in steep permafrost rocks at the scale of instability.