GNGTS 2014 - Atti del 33° Convegno Nazionale

108 GNGTS 2014 S essione 1.1 and spatial correlation it can be confused with interseismic signals or orbital errors. Thus, measurements of ground movements occurring on the different time scales of the earthquake cycle, from the nearly instantaneous deformation caused by seismic dislocations (Massonnet et al. , 1993), to the slow strains of the interseismic phase (Wright et al. , 2001) can be obtained using interferometric methods: DInSAR (Differential Interferometric Synthetic Aperture Radar) (Massonnet and Feigl, 1995) and MAI (Multi Aperture Interferometry) (Scheiber and Moreira, 2000; Bechor and Zebker, 2006) are suitable for the coseismic displacement, whereas multitemporal InSAR methods (Ferretti et al. , 2001; Berardino et al. , 2002; Hooper, 2007) with an accuracy of up to one millimeter per year over time periods of several years (Casu et al. , 2006), are suitable for small displacements over large temporal spans. We perform a large SAR data analysis focusing on the portion of the Emilia region affected by a seismic sequence during 2012. This area is located in the Po plain, which represents the east–west continental collisional boundary between the subducting Adria plate to the north, and the overriding Northern Apennine block to the south (Picotti and Pazzaglia, 2008). The 2012 seismic sequence occurred in the central Po plain tectonic domain, characterized by arcuate blind thrust systems and related growth folds located below the Plio-Quaternary sedimentary cover (Pieri and Groppi, 1981; Pieri, 1983; Consiglio Nazionale delle Ricerche, 1992; Burrato et al. , 2003), as also highlighted by several seismic sections (Boccaletti and Martelli, 2004). Based on geomorphological analysis, subsurface geology, seismicity, and present day stress field, many authors proposed the current activity of the frontal part of the Northern Apennine accretionary wedge (Meletti et al. , 2000; Valensise and Pantosti, 2001; Burrato et al., 2003; Scrocca et al. , 2007; Boccaletti et al. , 2010). Active fold growth in this area is describe by Burrato et al. (2003), which observe the northward migration of the Po River and other smaller watercourses during the Late Quaternary. Recent horizontal GPS measurements (Serpelloni et al. , 2006; Devoti et al. , 2011) suggest ~1 mm yr -1 of shortening, proving the active thrusting of the area. The Emilia sequence took place in an area of low historical seismicity. Since at least the year 1000 A.D. this area has never experienced earthquakes of magnitude larger than ML ~ 4.7 (1574 Finale Emilia earthquake, Rovida et al. , 2011). Larger magnitude earthquakes occurred west and east of the 2012 epicentral area. The coseismic deformation of two 2012 mainshocks, occurred respectively on May 20, 2012, Ml 5.9, and May 29, Ml 5.8, and were investigated analyzing COSMO-SkyMed and Radarsat-1 surface displacements as well as GPS observations (Pezzo et al. , 2013). The major finding of this work can be summarized as follows: i) The location of the coseismic deformation measured by InSAR data corresponds to part of the Mirandola and Ferrara folds, located under the Po alluvial plain. This evidence supports the long-term geomorphic analyses that attribute to the growth of the same folds the wide northward bend of the Po river course and the deviation of the Secchia and Panaro rivers (Burrato et al. , 2003); ii) The SAR data inversion results suggest that the main activated faults were the Ferrara thrust (May 20 event) and the Mirandola one (May 29 event); iii) displacement map analysis shows an aseismic deformation that the is well modeled by slip on the eastern side of the frontal Mirandola thrust, later activated during the May 29 mainshock; this aseismic pattern reasonable occurred in the time span between the two mainshocks. The short-term coseismic deformation observed during the seismic sequence together with inter- and post-seismic velocities showed in this work, may provide the opportunity to harmonize all geological long-term observations with the present day rates. Data availability. The available SAR dataset includes several overlapping COSMO- SkyMed image beams (Stripmap mode) as well as ERS and Envisat datasets for both ascending and descending tracks covering almost the entire Emilia Region (for details see Tab.1). We measured ground deformation rates adopting the SBAS technique (Berardino et al., 2002) for multi-temporal SAR Interferometry, using the Sarscape© software. We used both ascending and descending COSMO-SkyMed image datasets spanning the June, 2012- December, 2013 time interval to study the post-seismic deformation, as well as