GNGTS 2014 - Atti del 33° Convegno Nazionale

50 GNGTS 2014 S essione 1.1 main earthquakes (May 20 and 29, 2012) and for a COSMO-SkyMed (CSK) interferogram obtained from two descending acquisitions on May 27 and June 4, 2012 pair, encompassing only the May 29, 2012 event; multitemporal DInSAR measurements of the CSK data between June 4, 2012 and May 7, 2013, including about 1 one year of post-seismic deformation; GPS data describing coseismic and post-seismic deformations. This allows us to reduce ambiguities associated with each dataset and to better constrain the earthquake/fault associations, the geometrical features and the slip distributions of the two activated thrust faults. In addition, preliminary post-seismic deformation models will be presented for a better understanding of the strain relaxation processes in this region. The 2012 Emilia seismic sequence. The May 20M W 5.9 mainshock, occurred near the city of Finale Emilia, was preceded by a M L 4.1 foreshock 3 h earlier (Scognamiglio et al. , 2012). Following the mainshock an intense afterschock sequence occurred, with several events of magnitude M > 5. On May 29 a M W 5.8 located about 12 km SW of the May 20 mainshock occurred near the city of Mirandola. Moment tensor solutions of the main events (Pondrelli et al. , 2012; Scognamiglio et al. , 2012) exhibit thrust faulting with E-W oriented nodal planes, consistent with the direction of shortening shown in the interseismic geodetic data (Serpelloni et al. , 2006; Devoti et al. , 2011). The relocated aftershock distribution delineates a E-W trending structure extended for about 50 km, defining two separate segments with different dip from west to east. Govoni et al. (2014) estimate the dip of the western (the Mirandola thrust) and eastern (the Ferrara thrust) fault segments to be about 70° and 45° respectively. Geodeticdataset.High-precisionlevellingdata. Thehigh-precision levellingmeasurements were obtained from first-order double precision levelling surveys during different campaign periods. The pre-seismic levelling surveys, performed by a private company with the aim of planning a new regional highway, took place in April 2011, just one year before the seismic sequence. The post-seismic data were collected between April and May 2013, one year after the occurrence of the mainshocks (May 20 and 29, 2012) of the seismic sequence by the Istituto Geografico Militare (IGM). They consists of a levelling line oriented in a east- west direction, connecting two levelling lines of the first-order of the IGM. The total length of measured lines is 67 km, with 500 sites and a mean benchmark density of 7.4 benchmark/km. Post-earthquake levelling measurements followed high-precision levelling standards (Bomford, 1971) with mean errors well within the maximum tolerance admitted for first-order surveys. Since the IGM measurements started about one year after the mainshocks, the resulting displacements include coseismic and initial post-seismic deformation. The benchmark 52, west of the epicentres of the seismic sequence, close to Ferrara and outside the area of significant deformation according Fig. 2 – Geodetic sites in the Ferrara arc area: high-precision levelling lines (inverted triangles), GPS stations (black and grey squares) and RSAT-2 data sampled points. Solid lines are major faults of the area; solid red lines indicate the Ferrara arc system. The red stars indicate the May 20 and 29 mainshocks, while the green stars represent M > 5 events.