Gravitative deformation after the April 6 2009 L’Aquila earthquake detected by Cosmo SkyMed

We have investigated the post-seismic effects of the L’Aquila earthquake, that hit the city and the surround region on April 6, 2009. For this purpose, we have applied a multi-temporal InSAR technique and we have exploited the very high resolution SAR images acquired by the X-band sensor on board of COSMO-SkyMed (CSK) Italian satellite constellation. The series of CSK interferograms have allowed to retrieve the surface displacement field for a time span of 480 days after the main event. In particular, we have focused our attention on the understanding whether the measured Line of Sight (LOS) deformation might have been produced only by tectonic afterslip or if other causes have occurred. Data from previous studies and literature have highlighted the reactivation of pre-existing deep seated gravitational slope deformations (DSGSD) after great earthquakes. For the considered case study, the deformation map has showed a clear pattern of surface movements on the Mt. Ocre (south-west from L’Aquila city centre; figure 1) which, compared with geomorphological evidences on the Mt. Ocre ridge, has allowed to interpret the result as gravitational processes triggered by past seismic activity, that produced sackung type displacements. This suggests that part of the detected deformation is ascribable to gravitative processes triggered by the April 6 2009 mainshock. In order to confirm such hypothesis, a Finite Element Analysis of two cross sections along Mt.Ocre ridge has been performed. Two different analyses have been conducted considering both the elastic and the elastoplastic rheology of the involved materials. In particular, the numerical results from the elastoplastic rheology model are in good agreement with the measured data, highlighting also a nonlinear deformation of the Mt. Ocre ridge because of the yielding material. These outcomes enforce the hypothesis that the part of the postseismic deformation of Mt.Ocre ridge is caused by reactivation of pre-existing deep seated gravitational slope.