GNGTS 2013 - Atti del 32° Convegno Nazionale

1994 were Trimble 4000 SSE receivers and Trimble compact with ground plane (model 22020- 00) antennas. GPS data have been processed using the GAMIT/GLOBK software (Herring et al. , 2006) with IGS (International GNSS Service) precise ephemerides and Earth orientation parameters from the IERS (International Earth Rotation Service). We tied the measurements to an external global reference frame by including in our analysis the data from seven CGPS stations belonging to the IGS and EURA networks and operating since 1994 (GRAZ, HERS, JOZE, MADR, ZIMM). The quasi-observations were then combined with global solutions (IGS1, IGS2, EURA) provided by the Scripps Orbital and Permanent Array Center (SOPAC) at UC San Diego. The loosely constrained daily solutions were transformed into ITRF2005 (2005 International Terrestrial Reference Frame; Altamimi et al. , 2007) and then rotated into a fixed Eurasia frame. Preliminarily, the Eurasian velocity field shows that the two GPS stations south of the an- ticline (UNIG, S114) move with velocities ranging from about 4 to 7 mm/yr along NNW to NNE directions, whereas the station located north of the structure (TIRI) move to the SSW with velocity of about 2 mm/yr (Fig. 2). This results are consistent with NNW-SSE vectors obtained by permanent stations (Mattia et al. , 2012), related to the Africa-Europe convergence process (with the exception of the TIRI benchmark that could be affected by the dynamics of the volcano). Morphostructural data. New field surveys were performed with the aim to verify if ground deformation provided by satellite data agree with geological and morphological features. The Catania Anticline is located in a volcanic and strongly anthropized area. So, field evidence of active thrusting and folding is difficult to observe. However, preliminary results indicate that the differential ground motion provided by interferometric data (Lundgren et al. , 2004; Bonforte et al. , 2011) matches with the vertical deformation of the drainage network along the hinge of a large WSW-ENE trending anticline west of the urban area of Catania. Moreover, high resolution topographic profiles obtained by 2x2 m grid DEM show the occurrence of bulging coaxial with the hinge zone (Fig. 2). Information on geometric relationships between the growing anticline and the underlying thrust is lacking. However, thrust-related anticlines can be described by three end-member geometries, depending on the relationships between thrusts and the overlying anticlines: fault- bend folding, fault-propagation folding and detachment folding (see Storti and Poblet, 1997 and references therein). Combining the 5-6 mm/yr shortening across the anticline with the 10 mm/ yr of the corresponding uplift, the hypothetical slip on a unique shear surface would result on a >60° dipping plane. Such attitude is unrealistic for a thrust ramp, therefore we exclude fault- propagation folding or fault-bend folding models (Fig. 3). Conversely, kinematic models have shown how detachment fold model can account for uplift rate greater than shortening, in particular in the early stages of the anticline (Storti and Poblet, 1997). An incipient sub- horizontal detachment within the clayish foredeep deposits or at the top of the buried foreland sequence is clearly showed by seismic profiles (Torelli et al. , 1998). Discussion and conclusion. Geological and morphological anal- ysis, compared with seismological and geodetic data, suggest that a compressive regime currently oc- curs in the western sector of Mt. Fig. 3 – Kinematic model of detachment folding in the area south of Mt. Etna. 51 GNGTS 2013 S essione 1.1