COSMO-SkyMed X-band SAR imagery for detecting surface liquefaction induced by the 2012 Emilia Region (Italy) earthquakes
Bignami, Christian1; Chini, Marco2; Albano, Matteo3; Falcucci, Emanuela1; Gori, Stefano1; Modoni, Giuseppe3; Moro, Marco1; Pierdicca, Nazzareno4; Pulvirenti, Luca4; Saroli, Michele3; Stramondo, Salvatore1
1Istituto Nazionale di Geofisica e Vulcanologia, ITALY; 2Centre de Recherche Public - Gabriel Lippmann, LUXEMBOURG; 3University of Cassino and Southern Lazio, ITALY; 4Sapienza University of Rome, ITALY
On May 20, 2012, at 02:03 GMT, the Emilia region (North Italy) has been hit by a Magnitude 5.9 earthquake. The earthquake occurred in the northern boundary of the Apennine chain compressive area, interested by a moderate seismicity and where few historical earthquakes below Magnitude 6 were recorded. The earthquake caused some major damage and collapses of ancient and historical buildings in the villages within the epicentral region. Several minor quakes followed the main one, and on May 29, at 7:00 GMT, a second Magnitude 5.8 event occurred some km Westward the first event, along another seismogenic source roughly parallel to the May 20 fault. We investigated the surface effects caused by the two seismic events, by means of COSMO-SkyMed imagery. In particular, we exploited four images acquired in the period between April 1, 2012 and June 6, 2012. The information derived from SAR differential interferometry (DInSAR), interferometric coherence and image intensity, allowed the identification of some features related to the liquefaction phenomena induced by the earthquake. We observed that in urban area (in particular, the villages of Sant’Agostino and San Carlo) the loss of coherence is related to differential subsidence of buildings, whereas in rural areas the loss of SAR coherence corresponds to the subsidence of paleo-channels. In addition, DinSAR allowed to measure the amount of such subsidence, thanks to the very high resolution capability of COSMO-SkyMed. The SAR derived information have also been confirmed with in filed survey. Finally, the observed liquefactions have been assessed by means of geological and geotechnical characterization of soil. For this purpose, a liquefaction susceptibility analysis has been performed thanks to a series of geotechnical in situ tests retrieved in proximity of the subsidence areas. These investigations allowed identifying a sandy layer susceptible of liquefaction, located at about 6-8 meters in depth. This layer is probably responsible of the liquefaction phenomena observed along the paleo-channels, where the sandy layer raises to few meters below the ground level. A rough estimation of liquefaction-induced settlements has also been conducted; the estimated values are in agreement with the DinSAR measurements.