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.

Multiple Geophysical Techniques for Investigation and Monitoring of Sobradinho Landslide, Brazil

“…This may possibly happen because of the shorter duration of the ambient noise acquisition campaigns on landslides. A detailed discussion can be found at [62]. A similar phenomenon was observed by [63] at a clayey landslide where the results did not show any mark changes in dV/V.…”

Variation in Rayleigh wave ellipticity as a possible indicator of earthflow mobility: a case study of Sobradinho landslide compared with pile load testing

“…On the slope of the study area, the channel depositions in the basin are distinguished as (i) landslide debrites due to recent rotational failure mechanism; (ii) fluvial deposits on recent riverbanks as alluvial fan deposits, colluvial, and alluvial. The detailed geology and geomorphology of the area can be found elsewhere (Hussain et al, 2019c and references therein).…”

“…Ambient noise at each point was recorded for 30-minutes length in accordance with the guidelines provided by SESAME (2004). In the second stage, for continuous ambient noise recording, three sensors were installed on the landslide in a triangular geometry, as adopted by Hussain et al (2019c). The continuous data used for the seasonal impact evaluation was divided into three acquisition campaigns: (i) dry period, from 02-11-2016 to 08-11-2016; (ii) intermediate, from 12-04-2017 to 15-04-2017; and (iii) saturated period e.g.…”

“…In these studies (Mainsant et al, 2012;Bertello et al, 2018), a substantial drop of Rayleigh wave velocity has been observed in response to the earthflow acceleration, which is followed by a slow return to pre-disturbance of Rayleigh velocities as the landslide decelerates. However, these studies applied expensive, time-consuming and labor extensive techniques for the estimation of Rayleigh wave velocities such as time-lapse interferometry (Mainsant et al, 2012;Hussain et al, 2019c) and time-lapse active Multi-Channel Analysis of Surface Waves (MASW) (Bertello et al, 2018).…”

“…Rayleigh wave ellipticity calculated from an HVSR curve (Horizontal to Vertical Spectral Ratio) provides an alternative choice. Recently, few studies have interpreted seasonal changes in HVSR ellipticity curves as a result of the thaw-freeze cycles of an active permafrost layer (Abbott et al, 2016;Kula et al, 2018;Köhler and Weidle, 2019) and shallow rainfall-triggered landslide (Hussain et al, 2019c). The results of these studies have suggested that surface wave ellipticity (HVSR peak) might constitute a good indicator for the internal deformation and transition in material state (fluidization process) and can be used as a precursor for predicting earthflow.…”