GNGTS 2013 - Atti del 32° Convegno Nazionale

Since at the time of writing no reliable GPS time series were available for the post-seismic period, we validated the InSAR results by comparing the velocities in the overlapping areas. This procedure is possible because each velocity map is obtained using independent data from different orbits, but it is only qualitative, since the satellite-to-ground line of sights (LoS) are also different for each map. Frame B4 North. The map shows a post-seismic uplift pattern (in the LoS direction) of up to ~20 mm/yr in the area of the May 20 th , Mw=5.9 mainshock, corresponding to the top of the Ferrara thrust fold. We tentatively attribute the uplift observed in the area 5 km North of Finale Emilia to afterslip over the May 20 th fault plane, since: a) the displacement time series here show a nearly exponential trend typical of such local post-seismic signals; b) although decorrelation and noise are larger in the postseismic map, the similarity between the post-seismic mean velocity and the co-seismic displacement map (Pezzo et al. , 2013), is evident. Lower uplift rates are observed in the frontal part of the Ferrara arc (to the North of the mainshock), while to the South negative ground velocities are present in the Finale Emilia and the Reno paleo-channel areas. The latter is an area where widespread co-seismic lique- faction effects were observed after the May 20 th mainshock (Emergeo Working Group, 2013). The spatial correlation with these local co-seismic effects suggests that the high post-seismic Fig. 3 – (A): Wrapped Radarsat-1 interferogram spanning from May, 12th to June, 5th. The black rectangles represent the COSMO-SkyMed footprints; (B): Displacement map obtained by subtracting COSMO-SkyMed and Radarsat deformation fields. In the top-right corner a zoom of the area enclosing the aseismic transient occurred between the two largest shocks of the sequence (Pezzo et al. , 2013); (C): Post-seismic ascending COSMO-SkyMed ground velocity map (Beam 10h); (D): Displacement COSMO-SkyMed time series (red triangle in (C)). 206 GNGTS 2013 S essione 1.2