Typological analysis of slidequakes emitted from landslides: experiments on an expander body pile and Sobradinho landslide (Brasilia, Brazil)

Abstract

Reactivation of a landslide is usually accompanied by microseismic signals emitted from the deforming soil mass. The reproduction of similar signals in a physical model test conducted under control conditions can allow researchers to explore and test such complicated signals to improve the prediction of full-scale failure. The present study investigates the similarity between the slidequakes (microseismicity) naturally emitted from an existing colluvial landslide (Sobradinho, Brazil) in response to rainfalls and the emissions generated by a pullout test of an expander body (EB) pile in tropical soil under controlled conditions. The microseismic signals emitted from both experimental sites (i.e. the landslide and the EB pile test) were recorded and compared. Data were acquired by mini-arrays of four short-period seismometers. For the signal nomenclature, a typological scheme was adopted, in which sonograms/spectral contents of the signals were used. As a result, short duration microseismic signals were observed during the pullout test. In contrast, at the Sobradinho landslide, the testing detected signals of different characteristics whose source mechanisms have remained ambiguous, mainly because of the short duration of the data campaigns. However, at the landslide, propagating events were observed that might be attributed to the energies generated by the river bedload during the heavy rains. The present study offers some insight into the pre-collapse dynamic behavior of unstable slopes in clayey formations.

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

“…Nano-seismic monitoring (NM), which is based on emitted signal (ESb), has been used for the dynamic analysis of landslides [8,9] as well as characterizing their activity [10]. Using NM, the effects of rainfall-induced pore-pressure and water conditions (stiffness variations) on the dynamics of landslides have been discussed in the literature [7,11,12]. The landslide dynamics are studied in terms of detection, characterization and localization of weak energy signals, named "slidequakes" (earthquake type having short-duration and are found discernable, traceable wave packets).…”

“…In the case of a clayey landslide, brittle materials are absent so energy is not suddenly released in the event of a collapse. However, sometimes the signals recorded are related to the mechanical behavior of soil [7]. Therefore, these techniques (SEb) are better described in comparison to some ground truth data provided by other complementary techniques such as remote sensing of the landslide surface and extensometer data that can significantly increase their reliabilities.…”

“…The soil in the region is named as 'porous clays' having high porosity and low density which is formed as a result of high degree of weathering and leaching. Due to its high porosity and cementitious bond type, it becomes a highly unstable under increased moisture and/or changes in the state of stresses, almost always presenting a volume variation as high as the variation of these factors (referred to as a collapsed structure) [7].…”

“…These were exemplified by a case study conducted on Sobradinho landslide in Ribeirão Contagem fluvial valley, Brazil. The case study represents a prototype of shallow and rainfall-triggered landslide i.e., commonly occurring phenomena in the region [7]. The dynamic analysis included three different advanced seismic geophysical techniques based on ambient noise including Ambient Noise Interferometry (ANI), Horizontal to Vertical Spectral Ratio (HVSR), and Nanoseismic Monitoring (NM).…”

“…The small scale discontinuities of intermediate resistivity materials are also delineated on the section. The resistivity values suggest that they consist of relatively coarse-grained material, which may provide the pathways for the rainfall infiltrating water that may build pore water pressure in the landslide mass, that eventually, reactivating the landslide in the case of some future extreme rainfall events [7,23]. At the bottom, very low resistivity values were found that might be related to fine-grained material having a large amount of water (water table).…”