Time-lapse refraction seismic tomography for the detection of ground ice degradation
Time-lapse refraction seismic tomography for the detection of ground ice degradation
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DOI：
10.5194/tc-4-243-2010
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发表时间：
2010-07
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影响因子：
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通讯作者：
C. Hilbich
中科院分区：
文献类型：
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作者：
C. Hilbich
抽象的。地下冰含量是控制高山地区多年冻土退化自然灾害潜力的主要因素。因此，监测冰含量的变化与监测山区永久冻土层的温度同样重要。尽管电阻率断层扫描监测（ERTM）被证明是观察冰退化的一个有价值的工具，但结果往往不明确或受到反演伪影的污染。理论上，地震波的纵波速度对未冻水和冰之间的相位变化的敏感性与电阻率的敏感性相似。如果一般条件（岩性、地层、风化状态、孔隙空间）在观测期间保持不变，重复地震测量观测到的走时时间的变化应表明地下物质的孔隙和裂缝内的冰和水含量的变化。在本文中，时移折射地震层析成像 (TLST) 方法作为独立方法应用于瑞士阿尔卑斯山的两个测试地点的 ERTM。该方法的测试和验证基于以下内容：a) 时移地震图的比较和地震信号再现性的分析；b) 时移走时曲线相对于走时变化和纵波速度变化的分析；c) 反演断层扫描图的比较，包括速度变化的量化。结果表明，TLST 方法在检测冻融过程引起的地下条件变化方面具有很高的潜力。对于 3000 m/s 量级的速度变化，甚至可以明确识别显着的冰损失。
Abstract. The ice content of the subsurface is a major factor controlling the natural hazard potential of permafrost degradation in alpine terrain. Monitoring of changes in ice content is therefore similarly important as temperature monitoring in mountain permafrost. Although electrical resistivity tomography monitoring (ERTM) proved to be a valuable tool for the observation of ice degradation, results are often ambiguous or contaminated by inversion artefacts. In theory, the sensitivity of P-wave velocity of seismic waves to phase changes between unfrozen water and ice is similar to the sensitivity of electric resistivity. Provided that the general conditions (lithology, stratigraphy, state of weathering, pore space) remain unchanged over the observation period, temporal changes in the observed travel times of repeated seismic measurements should indicate changes in the ice and water content within the pores and fractures of the subsurface material. In this paper, a time-lapse refraction seismic tomography (TLST) approach is applied as an independent method to ERTM at two test sites in the Swiss Alps. The approach was tested and validated based on a) the comparison of time-lapse seismograms and analysis of reproducibility of the seismic signal, b) the analysis of time-lapse travel time curves with respect to shifts in travel times and changes in P-wave velocities, and c) the comparison of inverted tomograms including the quantification of velocity changes. Results show a high potential of the TLST approach concerning the detection of altered subsurface conditions caused by freezing and thawing processes. For velocity changes on the order of 3000 m/s even an unambiguous identification of significant ice loss is possible.