GNGTS 2013 - Atti del 32° Convegno Nazionale

deformation rates observed along the Reno paleo-channel, and at least partially also in Finale Emilia, could be related to the readjustment of the shallow acquifer level. Finally, an minor uplift of ~4 mm/yr is observed SE of Ferrara. This deformation shows a different sign in the frame B3 descending velocity map thus it may indicate the presence of a small component of horizontal displacement. In this case the movement would be W-directed, since the signals are positive in the ascending LoS and negative in the descending LoS. Frame B10h. This map shows also interesting mean velocity patterns. LoS uplift velocities up to ~18 mm/yr are evident in the surroundings of the Mw= 5.8 Mirandola aftershock, as well as minor negative velocities immediately to the South. This pattern follows approximately the extent of the coseismic deformation (Pezzo et al. , 2013) and can likely be attributed to afterslip along the same fault. In this map too we observe minor uplift North of the Mirandola thrust front. Moreover, few large, but very local subsidence patterns are also visible to the South (e.g. in Carpi); these patterns are not related to post-seismic deformation, and are due to long term ground movements caused by local acquifer depletion and/or shallow sediment compaction. Frame B03 descending. In this map we notice again the LoS uplift in the area of co-seismic uplift (East of Bondeno), and the strong negative velocities along the Reno paleo-channel, with similar values observed in the ascending Beam 4 North and Beam 4 center (not shown). The fact that in this area the ground velocities are similar on both the ascending and descending maps, indicates that most of the ground deformation here is occurring along the vertical direction. The time series in the area of maximum subsidence shows that most of the deformation occurred within 4-5 months from the mainshock. Ground deformation occurred before the start of the Emilia sequence. To investigate the inter-seismic phase in the area an Envisat-ASAR (C-Band) descending dataset of 37 images (10/02/2003-06/09/2010) has been processed using the SBAS algorithm. The obtained mean ground velocity map shows a maximum negative value of ~35 mm/yr around the cities of Bologna and Forlì. These patterns depend on well-known urban subsidence phenomena due to hydro-geological reasons and are not related to tectonic movements. Moreover, a positive (towards the satellite) ground velocity signal is visible close the area affected by the May, 2012 mainshocks. Discussion and conclusions. We analysed several different InSAR datasets of COSMO- SkyMed and ENVISAT images encompassing the Pollino and Emilia sequences of moderate seismicity. From a methodological point of view, the two test cases were very challenging. In the premises, the inherent difficulties of these test cases where: low deformation rates, probable presence of spatially and temporally complex deformation patterns, probable fast InSAR decorrelation between successive images due to vegetation and agriculture developments, short monitoring periods and limited size of the data sets (for COSMO), limited availability of the CGPS time series to be used for the correction of InSAR orbital artifacts. Eventually, we demonstrated the good capacities of time series InSAR techniques for the measurement of ground deformation patterns in these areas. Local, non tectonic deformation patterns were easily detected, as well as subtle patterns extended over larger spatial wavelengths. Quantitative validation by independent data could not be performed using CGPS, but qualitative validation using overlapping InSAR results gave in general good results. The COSMO-SkyMed coverage was temporally very discontinuous before the start of the Emilia sequence, and no good data set was available for possible pre-seismic deformation studies. However, an ENVISAT dataset of 37 images covering the temporal span 10/02/2003- 06/09/2010 and an ERS1/2 dataset of 36 images (30/09/1992-05/06/1999) were analyzed, and they did not show particular long-term deformation transients in the area interested by the 2012 Emilia sequence. 207 GNGTS 2013 S essione 1.2