Gravity driven and tectonic post-seismic deformation of the April 6 2009 L’Aquila Earthquake detected by Cosmo-SkyMed DInSAR

Abstract:

The present work focuses on the analysis of post-seismic surface deformation detected in the area of L’Aquila, Central Italy, after the strong earthquake that hit the city and the surrounding villages on April 6^th, 2009. The analysis has been carried out thanks to a new dataset of SAR COSMO-SkyMed images covering a time span of 480 days after the mainshock, with the adoption of the Persistent Scatterer Pairs (PSP) approach. This method allows the estimation of surface deformations by exploiting the SAR images at full resolution. In the investigated area two patterns of subsidence have been identified reaching a maximum value of 45 mm in the northeast area of the L’Aquila town. Here the subsidence is mainly ascribable to the post seismic slip release of the Paganica fault and it does not coincide with the maximum measured coseismic subsidence. The time series of the ground deformations also reveal that a large amount of deformation is released in the first three months after the main shock. The second pattern of deformation is centered on the Mt. Ocre ridge, where a detailed photogeological analysis allowed us to identify widespread evidence of morphological elements associated with Deep-seated gravitational slope deformation (DGSD). In particular geomorphologic analyses show evidences of lateral spread DGSD-type features, characterized by the tectonic superimposition of carbonatic sequences and transitional pelagic deposits. In this sector, the observed deformation is ascribable not only to the afterslip of the Paganica fault, but also to a gravitative cause. In order to confirm or reject such hypothesis a 2D numerical finite element models considering two cross sections over the Mt. Ocre ridge has been performed. The coseismic and postseimic deformations have been simulated numerically, considering an elastic-perfectly plastic rheology for the constituent rocks. First results show that most of the postseismic deformation is ascribable to the plastic deformation induced by the gravitative rebalancing of the ridge after the coseismic deformation.