Impacts on mountain settlements of a large slow rock-slope deformation: a multi-temporal and multi-source investigation

Many studies deal with the correlation between landslide velocity and damage degree of buildings or infrastructure. For shallow or moderate depth, slow landslides such as complex, slow flow or roto-translation type are well studied by InSAR or other ground-based instruments to retrieve a matrix correlation of velocity damage. However, few of them investigate the effects of deep-seated gravitational slope deformation (DsGSD) displacement. These phenomena usually have a very deep sliding surface, covering a vast area with constant velocity. This study investigates the building damage, mapped with a detailed field survey, correlated with one of the massive DsGSD of the Alps (Sauze d'Oulx DsGSD, NW Italy) affecting several villages. We used multi-temporal InSAR data and ground-based monitoring to obtain 26 years of displacement time series. The results show a complicated correlation, in which several factors influence the degree of building damage, such as the material of the building, their state of maintenance, the position on DsGSD, the depth of movement, the secondary process or the velocity range variability. A simple correlation with velocity is not exhaustive: the central part of DsGSD shows a higher velocity rate (up to 30 mm/yr), but with limited damage; while at the toe boundary of deformation, slow rate of movement produces more severe damage. These findings show that several in-depth studies should integrate velocity data from monitoring to assess the coexistence of these huge complex phenomena and define their impact on anthropic structures before making a risk assessment and a suitable land use planning of mountainous territory.