## 3 Materials and Methods
### Monitoring Network and Equipment  
The investigation of the factors controlling the kinematics of the landslide was guided by the antecedent monitoring results described above. Therefore, in June 2015, fixed automatic inclinometric probes were installed inside the four boreholes drilled after the reactivation occurred in winter 2014. This was carried out with the purpose of increasing the temporal resolution of subsurface displacement measurements through the acquisition of continuous data time-series. The automatic probes examined in this study were placed at the same depths as the main sliding levels detected during the previous monitoring phases conducted by means of traditional measurements. By considering the shape of prior horizontal subsurface displacement profiles, these unstable zones were assumed to be reasonably representative of the mobility across the whole thickness of the active portion of the accumulation. Specifically, the inclinometric sensors were positioned at a depth of 6 m in FON1, 12 m in both FON2 and FON3, and 24 m in FON4. According to the available stratigraphic logs (Figure 7), in the FON1 tube, the installed probe acquired deformations developing in a horizon of the landslide deposit consisting of clayey gravels (i.e., GC). In the FON2, FON3, and FON4 tubes, the sensors were placed in the proximity of the interface separating the landslide accumulation, consisting of either clayey sands (i.e., SC) or silty-clayey gravels (i.e., GM-GC), and the most weathered and de-structured bedrock levels (Figure 7). The automatic probes provide the amount of horizontal displacement by means of Hall element sensors that measure the inclination of the casing with respect to the vertical direction. The deviation from the vertical axis of the casing tube produces a change in magnetic flux density, which is detected from the Hall sensor in the form of voltage. The accuracy of the tilt angle readings is 0.5% in the \(\pm 10^{\circ}\) full-range scale, producing errors in displacement measurements of approximately \(\pm 0.1\) mm [68]. The temporal resolution of the displacement measurements was set to be hourly. During the examined monitoring period, the four verticals were also surveyed through a mobile biaxial inclinometric probe to detect deformations both above and below the continuously monitored levels. Therefore, four traditional measurements were also performed by temporarily removing the permanent automatic probes. During the measurements, the probe was lowered to the bottom of the casing tube and then raised incrementally in 1 m intervals. The accuracy of the traditional inclinometer equipment is \(\pm 2\) mm per 30 m of casing tube [69]. Figure 6: (**a**) Inclinometric profiles of local displacements over the period June 2014–May 2015; (**b**) cumulative displacement vector at the tube head. To monitor the pore water pressure, an automatic piezometric sensor was installed within the core destruction borehole P3, which was drilled close to the FON2 inclinometer tube. The pore water pressure sensor was positioned at a depth of 12 m below the ground surface, which corresponds to the location of the most marked displacement previously identified along the nearby FON2 inclinometer. The installed sensor consists of a piezoelectric element bonded to a flexible diaphragm; the deflection produced on the latter by the change in water pressure is detected by the transducer and converted into an electrical signal directly proportional to an absolute value of pore water pressure [70]. In the measurement section, the piezometric sensor was placed in a small sand-filled pocket of the drilled borehole, which was subsequently sealed-off with packed bentonite. The accuracy of the electric piezometer is 0.25% of full scale, which was 200 kPa in this case, giving an error of \(\pm\)0.5 kPa [71]. Each inclinometric and piezometer sensor was connected to a datalogger for measurement acquisitions. All monitoring systems are powered by a photovoltaic panel and include a wireless device for transferring measured data.