Terrestrial data and remote sensing technologies for monitoring a large-scale and low-kinematic landslide in a DSGSD ophiolitic landscape (Ligurian Apennines, Italy)

Deep Seated Gravitational Slope Deformations (DSGSDs) are complex phenomena usually triggered by a combination of genetic mechanisms, such as lithological, tectonic, geomorphological and climatic features. In Ligurian mountain the DSGSDs are frequent due to geologic setting and neotectonic activity. DSGSDs monitoring is a research field with significant implications either for scientific knowledge or for the most geo-engineering issues. The techniques of remote sensing have allowed in recent years to identify better these deep slope phenomena, which can feature different degrees of hazard. In this research, we present the monitoring activities of the large-scale landslides on which some villages of Upper Graveglia Valley (Entella river catchment) are settled (Brandolini et al., 2007). The Graveglia Valley is internationally recognized for its ophiolitic sequence with its sedimentary covers and the upper part of the catchment shows geomorphological evidences that could be linked to a DSGSD. For decades there have been reports of slope instability phenomena in the Upper Valley, outlined by several indirect kinematic indicators. Based on a project funded by Regione Liguria aimed at geohydrological risk reduction, drilling activities were carried out to identify the stratigraphy and set up a monitoring network (Faccini et al., 2019). An extensive geophysical survey was launched to plan the drilling survey, made by 10 boreholes: two inclinometer cases were installed (one with a robotized system) and eight piezometric cases. The monitoring instrumentation was completed with a weather station and two GPS benchmarks, to ensure a crosscheck of the displacements. The monitoring activities also included the use of PSInSAR satellite data over the period 1992-2019 (Allasia et al., 2021). The results of this study show a complex situation: an evolution of the large slope instabilities in several compartments with different kinematics, behaviour and depth of sliding surface and hydrogeological set-up is recognized. The monitoring data analysis also showed a good match between satellite, GPS, and inclinometric probe.