Analysis and interpretation of PSInSAR data for landslides mapping over large area: Giampilieri

In the last decade Persistent Scatterer InSAR (Synthetic Aperture Radar Interferometry) technique has improved its capability and its potential as land deformation measurement tools, providing precise measures of ground motions, demonstrating its suitability for detection and mapping of extremely to very slow moving landslides, both at a regional and local scale. In particular, available PSI data provide estimates of yearly deformation velocity, referred to both historical (1992-2001; ERS images) and present (2003-2009; ENVISAT images) scenarios, allowing both spatial and temporal characterization of the pre-existing landslide phenomena. In the late afternoon hours of October 1st 2009, a high intensity storm hit the Ionian coast of Sicily, particularly affecting the south-western part of the province of Messina, between the Peloritani Mountains ridge and the coastline. During of the night, the persisting rainfall in the coastal areas between Galati and Scaletta Zanclea (115 mm of rain in 3 hours recorded at Santo Stefano di Briga rain gauge) triggered slope failures, mainly shallow soil slides and debris flows on an area of about 40 km2. The worst damages were reported in the villages of Giampilieri, Scaletta Zanclea, Guidomandri, Pèzzolo, Altolìa, and Itàla. Landslides blocked many roads systems as well as the railway and main highway. The assessed number of fatalities caused by landslides and inundation amounts to 37 (including 31 deaths, six missing persons), with 122 injured people and the evacuation of 2.019 people. In the framework of the post-disaster activities leaded by the Civil Protection Authority, a detailed analysis of the pre-existing landslides affecting the whole territory hit by intense rainstorm was performed by the Earth Science Department of the University of Florence (Centre of Competence of the Italian Civil Protection for geohazards), exploiting the contribution of Persistent Scatterers Interferometry (PSI) technique and photo interpretation. Coupling and integrating deformation measurements extracted by means of PSInSAR technique, thematic maps (topographic and geological maps) and optical data (ortophoto, VHR optical satellite images and multi-temporal aerial photo), it is possible to identify twenty-six sites characterized by high hydro-geological hazard (Hotspot mapping). On the basis of available multi –interferometric data these sites were assessed as the most critical in terms of hydro-geological hazard, both for the type of instability events and / or extent of the detected phenomena and / or deformation velocities and / or presence of elements at risk. The outcomes of this integrated study, together with a proper urban planning will support future implementation of best strategies for risk mitigation, land use planning and consequent reduction of potential consequences on population, infrastructures damages and economic and social losses.