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

Abstract

The liquefaction phenomenon that occurred in the coseismic phase of th eMay 20,2012 Emilia(Italy) earthquake (ML5.9) is investigated. It was induced by the water pressure increase in the buried and confined sand layers.The level-ground liquefactionwastheresultofachaoticgroundoscillationcaused by theearthquakeshakingandtheobservedfailureswereduetotheupwardwaterflowcausedby the excessofporepressures.Weexploitedthecapabilityofthedifferentialsyntheticapertureradar interferometry (DInSAR)techniquetodetectsoilliquefactionsandestimatetheirsurfacedisplacements, as wellasthehighsensitivitytosurfacechangesofcomplexcoherence,SARbackscatteringandintensity correlation. Tothisaim,asetoffourCOSMO-SkyMedX-bandSARimages,coveringtheperiodApril 1–June 6,2012,wasused.Geological–geotechnicalanalysiswasalsoperformedinordertoascertainif the detectedSAR-basedsurfaceeffectscouldbeduetothecompactioninducedbyliquefactionofdeep sandy layers.Inthisregards,theresultsobtainedfrom13electricalconepenetrometertestsshowthe presence ofafinetomediumsandylayeratdepths,rangingbetween9and13m,whichprobablyliquefied during theearthquake,inducingverticaldisplacementsbetween3and16cm.Thequantitativeresults from geological–geotechnicalanalysisandthesurfacepunctualeffectsmeasuredbyDInSARareingood agreement, evenifsomedifferencesarepresent,probablyascribabletothelocalthicknessanddepth variability ofthesandylayer,ortolackofdeformationdetectionduetoDInSARdecorrelation.Theadopted approach permittedustodefinetheextentoftheareasthatunderwentliquefactionandtoquantifythe local subsidencerelatedtothesephenomena.Thelatterachievementprovidesusefulinformationthat must beconsideredinengineeringpractices,intermsofexpectedverticaldeformations.