GNGTS 2015 - Atti del 34° Convegno Nazionale

elliptical shape that is characterized, in correspondence of the epicentral area, by a maximum vertical displacement of some tens of centimeters. The application of satellite interferometry (DinSAR technique) and high-precision levelling (Bignami et al. , 2012; Salvi et al. , 2012; Caputo et al. , 2015) to the Emilia seismic sequence clearly documented the occurrence of this phenomenon; in particular, the main shocks of May 20 and 29 produced two uplifted areas, characterized by a maximum vertical displacement of about 25 cm, partly overlapping and with a cumulative length of about 50 km in an E-W direction. The recurrence of similar “areal morphogenic earthquakes” (Caputo, 2005) and the “competition” with the high subsidence and depositional rates that characterize the Po Plain, have progressively modified the geomorphology and stratigraphy of the region. In these conditions, the hydrographic network has proven to be particularly sensitive to vertical deformations, so even small altimetric and gradient changes led to river avulsions and diversions, highlighted by the presence of several drainage anomalies (Burrato et al. , 2003, 2012). Consequently, the alluvial plain is actually crossed by numerous abandoned river channels, some of which are still well preserved (Castiglioni et al. , 1999). Obviously, the presence of active tectonic structures responsible for the local uplifts and even for the complex interactions with the hydrographic network has influenced not only the distribution of the sediments on the surface, but also in the subsoil (down to some tens of meters) producing important stratigraphic variations and therefore also changes in the geophysical properties of the materials. Therefore, determining the uplift spatial distribution is crucial for reconstructing the recent tectonic evolution of the region as well as for understanding where active faults are located, and what is their possible seismogenic potential. With this premise, we planned a geophysical survey across some major tectonic structures affecting the subsoil of the eastern Po Plain, ���� �������� ��������� ��� ����������� ������� that possibly represent the seismogenic volumes of the above mentioned historical earthquakes� ��� ������������� ��������� �� � ������� . Our investigation consisted in a gravity survey carried out along a transect (Fig. 1b), ca. 170 km 2 and oriented SSW-NNE, i.e. almost perpendicular to the regional trend of the buried structures belonging to the central sector of the Ferrara Arc. Along a profile centered around the studied transect, in order to investigate the shallow subsurface (say, down to ca. 150-200 m), several passive seismic measurements of ambient noise were also performed, whose results are described and discussed in a companion paper (see Mantovani et al. , 2015). Fig. 1 – a) Simplified tectonic map of the buried northern Apennines showing the studied area (black boxes ESE of Ferrara. Modified from CNR-PFG, 1991). b) Location of the measured sites (blue dots) along investigated profile (black line). 128 GNGTS 2015 S essione 1.2