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（Abstract） 地球物理监测技术的应用，为解析斜坡在失稳触发因子作用下的动力学响应提供了可行途径。本研究采用环境噪声干涉法（Ambient Noise Interferometry）作为监测手段，分别针对巴西索布拉迪尼奥（Sobradinho）的人工缩尺垂直斜坡（受机械应力作用）与自然尺度滑坡（受降雨影响）开展监测。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，本研究采用动窗互谱技术，基于相对速度变化量确定了时移变化特征。针对该垂直斜坡，研究同时开展了地面激光扫描（Terrestrial Laser Scanning）以探测裂缝或裂隙的产生。原型实验结果显示，相对速度变化量呈下降趋势，在实验结束时达到-0.6%的最小值。由地面激光扫描影像生成的数字高程模型（Digital Elevation Model）未检测到任何变化，这是由于未出现厘米级浅表裂隙。在自然尺度滑坡（索布拉迪尼奥滑坡）场景中，无论是降雨日还是非降雨日，均未检测到相对速度变化量的显著变化，这主要是因为在数据采集的相对较短周期内，土体饱和度未发生足够明显的变化。