Monitoring of Sobradinho landslide (Brasília, Brazil) and a prototype vertical slope by time-lapse interferometry

Abstract The application of geophysical monitoring technologies may offer an opportunity to understand the dynamic of slopes in response to factors triggering their instability. In this study, Ambient Noise Interferometry was used as a monitoring approach on a man-made reduced-scale vertical slope and on a natural-scale landslide in Sobradinho (Brazil), under the influence of mechanical stress and rainfall, respectively. For both experiments, we adopted similar data acquisition system and processing workflow. After preprocessing of ambient seismic noise, the time-lapse changes were determined in terms of relative velocity changes using the moving window cross spectral technique. For the vertical slope, terrestrial laser scanning was also performed to detect crack or fissure generation. The prototype experiment results showed a decreasing trend of relative velocity changes and reached a minimum value of -0.6% at the end of the experiment. No change was detected on the digital elevation model that was computed from terrestrial laser scanning images, due to the absence of centimeter scale superficial fissures. At natural scale (Sobradinho landslide), no significant variation in relative velocity changes was detected for the rainy and non-rainy days, mainly because of the inadequate change in the degree of saturation, which was found within a relatively short period of data acquisition.

摘要 地球物理监测技术的应用，为探究斜坡失稳触发因子响应下的斜坡动力学特性提供了可行路径。本研究分别针对人工缩尺垂直斜坡，以及巴西索布拉迪尼奥（Sobradinho）的天然规模滑坡，采用环境噪声干涉法（Ambient Noise Interferometry）作为监测手段：前者受机械应力作用，后者受降雨影响。两项实验均采用了一致的数据采集系统与处理流程。在对环境地震噪声完成预处理后，借助移动窗互谱技术，通过相对速度变化量表征了时移变化特征。针对垂直斜坡实验，同步开展了地面激光扫描（terrestrial laser scanning）以监测裂隙生成情况。原型实验结果显示，相对速度变化量呈下降趋势，实验末期达到-0.6%的最小值。由于未出现厘米级表层裂隙，由地面激光扫描图像生成的数字高程模型（digital elevation model）未检测到任何变化。在天然尺度（索布拉迪尼奥滑坡）场景下，降雨日与非降雨日的相对速度变化量均未出现显著差异，这主要源于数据采集周期内，边坡饱和度未发生足够明显的改变。