Christian Ambrosi

Interpretation of Aerial Photographs and Satellite SAR Interferometry for the Inventory of Landslides

An inventory of landslides with an indication of the state of activity is necessary in order to establish hazard maps. We combine interpretation of aerial photographs and information on surface displacement from satellite Synthetic Aperture Radar (SAR) interferometry for mapping landslides and intensity classification. Sketch maps of landslides distinguished by typology and depth, including geomorphological features, are compiled by stereoscopic photo-interpretation. Results achieved with differential SAR interferometry (InSAR) and Persistent Scatterer Interferometry (PSI) are used to estimate the state of activity of landslides around villages and in sparsely vegetated areas with numerous exposed rocks. For validation and possible extension of the inventory around vegetated areas, where InSAR and PSI failed to retrieve displacement information, traditional monitoring data such as topographic measurements and GPS are considered. Our results, covering extensive areas, are a valuable contribution towards the analysis of landslide hazards in areas where traditional monitoring techniques are sparse or unavailable. In this contribution we discuss our methodology for a study area around the deep-seated landslide in Osco in southern Switzerland.

Valley shape influence on deformation mechanisms of rock slopes

Abstract Stress distribution in mountainous areas is influenced by local morphology. Valley morphology and the relationship between main and tributary valleys strongly depend on geological characteristics and evolution. They may control the evolution of slope instabilities, especially when interacting with pervasive structural features. We performed parametric three-dimensional (3D) numerical modelling of simplified slope geometries with variable slope angle (from 21° to 35°), length, combining different orientations for different slope sectors and changing attitude of pervasive planes of anisotropy (foliation, schistosity, bedding). Data used in the 3D models are the initial slope geometry, rock mass properties and internal anisotropy. We assumed Mohr–Coulomb behaviour, with the presence of ubiquitous joints and different piezometric levels. The model results show that plastic deformation initiates near the highest ridge just after deglaciation commences. A shear zone develops and propagates toward the toe of the slope, and its shape is strongly controlled by slope geometry, anisotropy and in situ stresses. The thickness of the failing mass, for model slope reliefs up to 3200 m, increases from 50 m to some hundreds of metres during glacier retreat, and it depends on geometry of slopes, anisotropy and in situ stresses. Results are compared to examples of deep-seated slope deformations from the Alps, which helps in the interpretation of such phenomena and in the understanding of their influence on valley evolution.

Monitoring slow mass movements with the Permanent Scatterers technique

In this paper we wish to show a few exemplificative results obtained in the framework of a wide area Permanent Scatterers analysis financed by Regione Lombardia. The core purpose was the identification and description of slope instability/failure phenomena in a relevant part of the Lombardy alpine territory (Northern Italy).

MONITORING AND ASSESSING THE STATE OF ACTIVITY OF SLOPE INSTABILITIES BY THE PERMANENT SCATTERERS TECHNIQUE

The evaluation of the state of activity is an essential step for landslide hazard assessment. To attribute a state of activity class to a landslide a suitable set of monitoring data is needed. Different types of landslides present different characteristics and are subjected to different spatial and temporal evolution; these become relevant when working at a regional scale or when a catastrophic evolution of the movement is expected. The Permanent Scatterers (PS) technique is used to determine state of activity and long term behavior of rock slope instabilities. The PS technique, overcomes several limitations of conventional differential SAR interferometry (DInSAR) applications, and proves to be effective for high accuracy monitoring of gradual very slow slope deformation which may eventually transform into extremely rapid failures. The success depends on various factors including: available data, location and morphology of the area, PS density; and motion of the targets. We present the results of the application of the technique at a regional scale in the Central Italian Alps involving different types of instabilities in different materials. The utility of the technique in landslide hazard assessment is demonstrated by the quality of the results and by theintegration of different datasets (inventory maps, site investigations, remote sensing).

GIS-based Calibration of MassMov2D

34 Pags., 3 Tabls., 9 Figs. The definitive version is available at: http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1467-9671