## 5 PSI by Means of TSC: Results and Discussion
### PSI Displacement Results
Some field inspections have been carried out confirming the existence of such indicators as structural disturbance, tension cracks, depressions filled with sediments, covered by vegetation, as well as tilted and rotated blocks, with weathered surfaces. At this stage, some ground-truth data are presented in order to validate the PSI results obtained. Figure 15 shows the inclinometric results in the borehole _S10_, which corresponds to the maximum displacement rate area of the lower part of the landslide (Cal Borro-Cal Ponet). The location of the borehole S10 is indicated in Figure 1b, seen in Section 2. In addition, this location has been also highlighted with a white spot in the PSI result figures (Figures 13 and 14). Inclinometers are geotechnical devices for measuring horizontal displacements affecting the shape of a guide casing embedded in the ground. They provide the displacements undergone in two orthogonal planes, and this information allows obtaining the real 3D ground displacement vector of movement. It is worth mentioning that in order to obtain reliable estimations, the end of the guide casing must reach a stable reference. The technique consists of obtaining relative displacements profiles over time by repeating measurements at the same depths. This measures may be compared in order to detect the possible displacements undergone along the different measurement campaigns. Moreover, recording the magnitude of displacements at different reading depths is useful to identify shear bands and different units of movement. The most common way to analyze inclinometric results is based on displaying the cumulative lateral displacement along different depths, starting at the bottom of the casing and integrating increments of displacement for all depths up to the ground surface. Figure 15 illustrates the deformed shape of the inclinometer casing along the borehole for different periods. Concretely, the curves available correspond to the period from December 2010, to October 2011, all referring to July 2008. The profiles plotted correspond to the maximum displacement axis (down-slope direction). Since the displacement is produced along the steepest gradient of the slope, the orthogonal axis did not record any displacement, and for this reason, it has not been represented in the figure. As indicated by the S-shaped plot, the main shear band is located at roughly \(30\) m under the surface of the landslide. The upper part of the plot has been amplified to compare the inclinometric results with the ones obtained using PSI techniques. The displacement undergone by the inclinometer between the period corresponding from December 2012 to October 2013, coinciding with the PSI processing, corresponds to \(1.8\) cm. Since the inclinometric results are given in an horizontal plane, these must be divided by the cosine of the slope angle in this area (\(\sim\)20\({}^{\circ}\)) in order to obtain the total down-slope displacement \(\sim 1.8\,cm/\cos(20^{\circ})=1.91\,cm\). This is equivalent to a total of roughly \(2.3\) cm/year. The results provided by the SAR sensors register \(\sim\)2.5 cm/year in this region, thus showing high agreement with the ground truth available. As mentioned above, some geological evidence observed recently also corroborates the displacement results retrieved. Figure 16 presents some photographs obtained during several field inspections carried  
Figure 15: Inclinometric results in the borehole S10 (Cal Borrö-Cal Ponet). out during \(2013\)-\(2014\). Figure 16a shows a picture of the interior of a famous house built in the mid-nineteenth century, near the area of maximum displacement of Cal Borro-Cal Ponet. The curved shape of the wall evidences the presence of displacements in the area. Figure 16b shows a picture of several cracks and shear openings along the road pavement, which have also appeared close to this area. Figure 16c shows curved trunks belonging to trees that have been subjected to a progressive tilt at the base, forcing the trunk to adopt this curvature in order to point vertically.