GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 1.1 51 to InSAR and GPS results (Serpelloni et al. , 2012; Pezzo et al. , 2013; Tizzani et al. , 2013) has been selected as reference benchmark for the levelling lines. The levelling lines describe the uplifted area of the hanging-wall blocks of the faults of the Ferrara arc on the basis of 92 measurements (Fig. 2). In particular the hanging-wall uplift is well constrained on the hanging-wall of the westernmost system, the Mirandola system, where the uplift reaches maximum values of about 18 cm. This main uplifted area is in good agreement with the elongated E-W displacement observed by InSAR data (Fig. 2) near the May 29 epicenter, where previous works (e.g., Pezzo et al. , 2013) observed a maximum displacement of ~14 cm. However, westwards of Mirandola city, where the lobe of InSAR displacement field tends to decrease, we observe an additional amount of uplift. This extra uplifted region could be due to the combined effects of the occurrence of the greatest aftershocks (M > 5) and early post-seismic deformation. On the easternmost part of the levelling lines, near Finale Emilia, the observed smaller peak of uplift well correlates with the eastern termination of the InSAR lobe of deformation near the May 20 epicenter. InSAR data. In this work we used SAR data acquired with RADARSAT-2 and COSMO- SkyMed satellites. In particular, we used the April 30, 2012/June 17, 2012 pair, acquired from RADARSAT-2 (RSAT2) descending orbit to measure the cumulative coseismic ground displacements due to the two main shocks (May 20 and 29) and the May 27, 2012/June 4, 2012 pair, acquired from COSMO-SkyMed (CSK) descending orbit to obtain the coseismic displacement field related to the May 29 earthquake. To measure the post-seismic deformation we used the radar surface displacement time series generated by applying a SBAS DInSAR processing algorithm to the data acquired from COSMO-SkyMed constellation between June 4, 2012 and May 7, 2013. This temporal interval starts 5 days after the May 29 main shock and includes about one year of post-seismic deformation (Fig. 1). The cumulative coseismic deformation field along the RSAT2 line-of-sight presents two main lobes due to the May 20 and 29 events, with a maximum displacement of about 15 cm corresponding to a sensor-target range decrease (Fig. 2). On the other hand, the CSK interferogram yielded only a main lobe due to the May 29 event, with a maximum displacement of about 8 cm towards the satellite. The discrepancies between the different interferograms are due to the different look angles and orbits. The displacement pattern in the CSK post-seismic interferogram, covering about one year of post- seismic deformation, shows one major lobe of decreasing line-of-sight displacements towards the satellite, with a maximum value of about 2- 3 cm, that approximately appears to overlap with the westernmost termination of the area of the May 29 coseismic displacements (Fig. 2), slightly shifted to the west (Fig. 3). This uplifted region appears to correlate with the area in which we observe some amount of additional uplift from levelling measurements. GPS data. Coseismic and initial post-seismic displacements have Fig. 3 – Geodetic sites in the Ferrara arc area. The circles show the CSK post-seismic data points, while the white triangles the distribution of levelling benchmarks. Other symbols as in Fig. 2.