Earthquake-induced Landslides Mapping By Combined Analyses Of Satellite DInSAR And Optical Data: The 24th August, 2016 Amatrice Earthquake (Italy).

On the 24th August, 2016 Central Italy was struck by a Mw 6.0 earthquake with an epicentral area near the city of Amatrice. Several landslides were triggered by the shaking in an area circa 30km in radius from the epicentral area (http://www.ceri.uniroma1.it/index.php/web-gis/cedit/). Aiming at support the detection and mapping of earthqhake-induced landslides, Satellite DInSAR technique (Differential Synthetic Aperture Radar Interferometry) combined with satellite and aerial high resolution optical imagery was used. Specifically, Sentinel-1, COSMO-SkyMed and ALOS-2 (both ascending and descending) co-seismic differential interferograms were used in combination with optical datasets available through the Copernicus Emergency Management Service. Interferograms have been analysed firstly with un-supervised analyses, based on the detection of the fringes anomalies, i.e. particular patterns of the interferometric phase such as: i) irregular shaped fringes, ii) abrupt interruptions of the of regional co-seismic fringes, iii) localized changes in the fringes gradient. Then, fringes anomalies have been analysed in order to detect landslide-candidates according to the following criteria: i) fringes anomalies must be located in slope areas; ii) the mean coherence values of the fringes anomalies must behigher than a predefined threshold; iii) fringes anomalies are present in more than one interferogram. Finally, the landslide-candidates have been validated by a combined expert analysis with satellite and aerial optical images and field evidences included in the catalogue of Earthquake-induced ground failures in Italy (CEDIT). By combining Optical and SAR images, more than 60 landslides were detected, 8 of which recognized only thanks to fringes anomalies. As a matter of fact, slopes affected by small plastic deformations (from mm to cm order) cannot be recognized by the interpretation of optical images that, on the other hand, are the only ones able to detect small scale slope failures such as rockfalls. Further steps in this study will be the intergration of remotely sensed landslides in the catalogue of Earthquake-induced ground failures in Italy (CEDIT) and the analyses of the data available from the earthquakes occurred in Central Italy in October 2016.