GNGTS 2014 - Atti del 33° Convegno Nazionale

shortening, postglacial isostatic rebound, flexural response to climate-driven denudation and rapid glacier shrinkage. The observed uplift in the northern Apennines, with rates mostly lower than 2 mm/yr, is consistent with the results obtained by repeated leveling surveys carried out over 129 years by I.G.M.I.(e.g. D’Anastasio et al., 2006) This uplift is also consistent with the effects expected from the longitudinal shortening of the belt (e.g., Mantovani et al., 2009, 2011, 2012; Cenni et al. , 2012, 2013). Some sites �� ��� �������� ��� ������� ������� �� ��� in the northern and central sectors of the Apennines chain are characterized by a slow subsidence. These displacements are actually analyzed in order to understand the causes. In particular, we are investigating the influence of ITRF2008 reference frame, or a possible correlation with the characteristics of the sites where the permanent stations are located. Significant subsidence, with velocities up to 5-10 mm/yr, is observed in the eastern Po basin while minor (negative or positive) vertical movements are recognized in the western Po basin. The comparison between the results obtained by this high density GPS network and those previously (until 2006) acquired by different techniques (Baldi et al., 2009, 2011; Bonsignore 2008) indicates that the rates are stable or in some cases are decreasing. SAR data analysis . The Synthetic Aperture Radar interferometry (SAR) technique has been widely applied to map subsidence phenomena in the Po Plain using advanced multitemporal approaches (e.g Bonsignore, 2008; Bitelli et al., 2014a; Bock et al., 2012; Meisina et al., 2008; Stramondo et al., 2007; Teatini et al., 2012). Recently the displacements obtained analyzing SAR satellite interferograms have been made available in the website of National Geoportal (NG) managed and supported from the Ministero dell’Ambiente e della Tutela del Territorio e del Mare. The data acquired by ESA ERS-1/2 and ENVISAT-ASAR platform have been used in the NG project in order to estimate the displacements of Permanent Scatter (PS) (Ferretti et al., 2001) along the satellite line of sight (LOS). This technique allows to overcome some limitations related to conventional SAR interferometry approaches (which may contain temporal and geometrical decorrelation phenomena) and to estimate the contributions of phase related to changes caused by the atmosphere between the different acquisitions. The satellite SAR interferometry (InSAR) can achieve very good results in the monitoring of ground deformation, especially in urbanized areas that, in the presence of buildings and infrastructure, have high reflective properties of the radar signal. In the case of agricultural areas, buildings and artifacts scattered permit the presence of radar target and then the satellite monitoring of the deformations. Therefore, the Fig. 3 – Distribution of vertical extensometers and GPS permanent stations in the Po Plain. Circles and yellow triangles indicate GPS and vertical extensometrs sites respectively. The colour of the circle s points out the value of the vertical velocity shown in Fig. 2 as indicate in the coloured scale. GNGTS 2014 S essione 1.2 137