Coseismic liquefaction phenomenon analysis by COSMO-SkyMed. 2012 Emilia (Italy) earthquake

tThe liquefaction phenomenon that occurred in the coseismic phase of the May 20, 2012 Emilia (Italy)earthquake (ML 5.9) is investigated. It was induced by the water pressure increase in the buried andconfined sand layers. The level-ground liquefaction was the result of a chaotic ground oscillation causedby the earthquake shaking and the observed failures were due to the upward water flow caused bythe excess of pore pressures. We exploited the capability of the differential synthetic aperture radarinterferometry (DInSAR) technique to detect soil liquefactions and estimate their surface displacements,as well as the high sensitivity to surface changes of complex coherence, SAR backscattering and intensitycorrelation. To this aim, a set of four COSMO-SkyMed X-band SAR images, covering the period April1–June 6, 2012, was used. Geological–geotechnical analysis was also performed in order to ascertain ifthe detected SAR-based surface effects could be due to the compaction induced by liquefaction of deepsandy layers. In this regards, the results obtained from 13 electrical cone penetrometer tests show thepresence of a fine to medium sandy layer at depths, ranging between 9 and 13 m, which probably liquefiedduring the earthquake, inducing vertical displacements between 3 and 16 cm. The quantitative resultsfrom geological–geotechnical analysis and the surface punctual effects measured by DInSAR are in goodagreement, even if some differences are present, probably ascribable to the local thickness and depthvariability of the sandy layer, or to lack of deformation detection due to DInSAR decorrelation. The adoptedapproach permitted us to define the extent of the areas that underwent liquefaction and to quantify thelocal subsidence related to these phenomena. The latter achievement provides useful information thatmust be considered in engineering practices, in terms of expected vertical deformations.