GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 1.2 229 the profiles, so that the velocity of profile B would be expected to be about 90% of that of profiles D. A curved pattern centered on the rotation pole is also expected. None of these signals are visible (see also Fig. 3), implying that the faults splaying from the North Anatolian fault to the north might also generate a non neglegible perturbation of the simple geometry of Euler rotation. Profile E0 - E1: samples the large scale deformation across the Trans European Suture Zone (TESZ), a major structural divide between Precambrian Europe to the northeast and Phanerozoic terranes to the southwest. The TESZ separates the Precambrian terranes of the Baltic shield and east European craton (EEC) from the younger terranes to the south and west (Thybo et al., 1999). The profile was chosen in analogy with the Polonaise 97 P4 seismic refraction profile (Grad et al., 2003). As Fig. 2a and Fig.3 suggest, there is vitually no change of the interpolated GPS velocities projected along the profile, implying that no deformation takes place, at least at or near the surface. Profile F0 - F1: shows the negative velocity gradient moving South to North, associated to the indentation of the Adria promontory/microplate. There is a vast literature on the subject and the velocity of indentation has been estimated by various authors, as well as the mechanical and thermal aspects of the indentation (see e.g. Caporali et al., 2013). Profiles G0 - G1 and H0 - H1: show the velocity drop associated to the closure of the Adria sea and the subduction below the Dinarides. Kastelic and Carafa (2013) have investigated in detail the implications of the velocity drop in models of the Adria subduction,and argued in favor of Adria as a seismically active and deformable lithospheric block. Fig. 2b and Fig. 3 (bottom) address quantitatively the velocity field associated with the eastwards extrusion of the region comprised between the PAL to the south and the SEMP/MMZ to the north. There is evidence that the process is active at present with a velocity change of ca. 1.8 mm/yr across a 300 km profile, implying a modest shear strain rate of some 6 nstrain/ year. The data are necessarily limited by the scarcity of GPS sites and the size of the signal. The velocity pattern is in any case consistent with a kinematics of lateral extrusion approximated by an extrusion-spreading model towards an unconstrained Pannonian basin acting as stress sink, as suggested by Ratschbacher et al. (1991a) and is probably driven by the indentation of the Adria block shown in Profile F. Conclusion. The analysis of the CEGRN GNSS data accumulated in the period 1996 – 2017 and carried out following the most recent procedures, software and ancillary IGb08/IGS14- based data (orbits, clocks, antenna models) has resulted in a homogeneous set of velocities that spread across Central Europe. The deformation regime is expected to be small, but non negligible. We report a widespread stretching of the crust in South Central Europe, bordering the Black Sea, associated with the dragging by the Anatolian anticlockwise rotation accompanied by lateral splay. We estimate that the N-S extensional strain rate measured by GNSS geodesy is consistent with an Andersonian traction driven solely by topography, over a time interval of ca. 6000 ± 1000 years. Compression is clearly visible wherever the Adria block moves relatively to the Dinarides and the South Eastern Alps. The lateral extrusion of the Eastern Alps is observed as an inversion of the velocity relatively to the SEMP shear zones to the north. Using a simple analytical model for the velocity across the profile we estimate a locking depth of 18 ± 4 km, which would imply that the slip associated with the extrusion is accommodated mostly in the upper crust. Finally, the TESZ seems subject to very small strain, if none. Acknowledgment. The Authors gratefully acknowledge the review of G.V. Dal Piaz of the early version of the manuscript. References Basili R., Kastelic V., Demircioglu M. B., Garcia Moreno D., Nemser E. S., Petricca P., Sboras S. P., Besana-Ostman G. M., Cabral J., Camelbeeck T., Caputo R., Danciu L., Domac H., Fonseca J., García-Mayordomo J., Giardini D., Glavatovic B., Gulen L., Ince Y., Pavlides S., Sesetyan K., Tarabusi G., Tiberti M. M., Utkucu M., Valensise G., Vanneste K., Vilanova S. and Wössner J.; 2013: The European Database of Seismogenic Faults (EDSF) compiled in the framework of the Project SHARE. http://diss.rm.ingv.it/share-edsf/ doi: 10.6092 /INGV.IT -SHARE-EDSF.