Synergic use of satellite and ground based remote sensing methods for monitoring the San Leo rock cliff (Northern Italy)

- On February 27th 2014 an entire portion of the rock massif on which the historic town of San Leo (northern Italy) is located collapsed. A monitoring system based on remote sensing techniques such as radar interferometry (PS-InSAR and GB-InSAR) and terrestrial laser scanning was planned, with the aim of monitoring the ground deformation evolution of the study area and assess the landslide residual risk.
- The PS-InSAR technique allowed to perform a pre- and a post-event displacement analysis on the general rock massif stability, evaluating the state of activity of long-term ground displacements.
- The GB-InSAR one year monitoring campaign allowed to analyse the short-term behavior of the 2014 event deposits.
- TLS data provided 3D temporal variations of the analysed rock wall, providing evidence of an ongoing rock block toppling at the base of the monitored rock cliff, also providing the detection of seven distinct block falls, and their volume assessment.
- The San Leo area is characterized by complex geomorphological and geometric features, different ongoing landslide processes with various state of activity. The combined use of the abovementioned techniques, thanks to the different employed instruments characteristics allowed to overcome the limitations of each single employed technique.

The historic town of San Leo (Emilia Romagna Region, northern Italy) is located on top of an isolated rock massif above the Marecchia River valley hillside. On February 27th 2014, a northeastern sector of the massif collapsed; minor structural damages were reported in the town and a few buildings were evacuated as a precautionary measure. Although no fatalities occurred and the San Leo cultural heritage suffered no damage, minor rock fall events kept taking place on the newly formed rock wall, worsening this hazardous situation. In this framework, a monitoring system based on remote sensing techniques, such as radar interferometry (both spaceborne and ground-based) and terrestrial laser scanning, was planned in order to monitor the ground deformation of the investigated area and to evaluate the residual risk. In this paper the main outlines of a 1-year monitoring activity are described, including a pre-event analysis of possible landslide precursors and a post-event analysis of the displacements of both the collapse-affected rock wall sector and the rock fall deposits.