GNGTS 2015 - Atti del 34° Convegno Nazionale

mechanism cannot account for a basic feature of the GPS velocity field (Fig. 1), i.e. the fact that the Apennine belt moves almost uniformly roughly NE-ward from the southern Apennines to the northernmost Apennines. Another major problem of the slab roll-back mechanism is explaining some major features of the GPS velocity field in Calabria and Sicily, i.e. the belt sectors where the presence of a well developed slab is documented by the distribution of deep seismicity. In particular one should explain why in the first zone the vectors are parallel to the main axis of the belt (Fig. 1 and e.g., D’Agostino et al. , 2011), and in Sicily the vectors are oriented roughly northward, towards the Tyrrhenian basin, i.e. about opposite to what happen in the northern Apennines. In summary, it seems very difficult to understand why the invoked slab pull mechanism induces very different or even opposite effects in the various sectors of the trench zone. The geodynamic interpretation proposed by Mantovani et al. (2009) and Viti et al. (2011) for the central Mediterranean region provides that the compressional regime induced by the convergence of the confining plates (Nubia, Eurasia and Anatolia-Aegean system) causes the outward escape of the Calabrian and Hyblean wedges with respect to the Apennine-Maghrebian belt, as sketched in Fig. 3. It is worth noting that such long-term kinematic pattern, involving a roughly ENE ward motion of the Calabrian Arc and a roughly northward motion of the Hyblean wedge, is very similar to the short-term one derived by geodetic data (Fig. 1). Conclusions. The present kinematic pattern of the Italian region, tentatively inferred from continuous GPS observations in a relatively high number of sites, provides significant insights into the geodynamic/tectonic setting in the central Mediterranean area. A significant number of data in the Apulian zone clearly indicate that the southern Adriatic domain moves roughly NE- ward. This evidence creates a problem if the Nubia-Eurasia relative motion is taken from global kinematic models, since it implies a significant relative motion between Adria and Nubia, in contrast with the fact that no clear decoupling zone can be recognized between such plates. It is difficult to believe that the expected relative motion between the southern Adria domain (moving roughly NE-ward) and the adjacent Nubia domain (moving about NNW- ward, following the NUVEL 1 model) only causes significant seismotectonic activity in the Gargano zone, a small sector of the southern Adriatic platform (e.g., Argnani, 2006). This major difficulty may imply that the Nubia-Eurasia rotation pole derived by global kinematic models is not reliable. This possibility is also suggested by the fact that the trend of the Nubia-Eurasia relative motion provided by the above models (NNW- to WNW-ward) cannot account for other major Quaternary tectonic features in the whole Mediterranean area, which rather suggest a NNE-ward trend of the Nubia-Eurasia relative motion (Mantovani et al. , 2007). To explain why the Nubia-Eurasia pole provided by global kinematic models may be not reliable, Mantovani et al. (2007) argue that the plate configuration adopted by such investigation is oversimplified, since it involves a two plates model (Nubia and Eurasia), notwithstanding that the distribution of seismic and tectonic features in the Mediterranean regions strongly suggests the presence of two microplates (Morocco and Iberia, Fig. 1), not moving in close connection with the Nubia and Eurasia main plates. To overcome the above difficulties, Mantovani et al. (2007) have proposed an alternative kinematic model (Fig. 1), which provides that Nubia moves roughly NNE-ward in the central Mediterranean region. This hypothesis does not involve significant difficulties, since it may account for the motion of the southern Adria domain derived by GPS and other data, it is compatible with the Mediterranean long-term evidence mentioned by Mantovani et al. ( 2007) and can also be reconciled, within errors, with the north Atlantic kinematic constraints, if the proposed four plates configuration is taken into account (Mantovani et al. , 2007). The GPS velocity field (Fig. 1) clearly defines the kinematics of two Adriatic zones, one located in the southern part (Apulia) and the other located in the northernmost Adria domain (Venetian plain). If such kinematic constraints are interpreted as related to a rigid structure, the resulting Adria-Eurasia rotation pole would be located in the western Alps, implying an independent motion between Nubia and Adria, whatever Nubia-Eurasia Euler pole is adopted GNGTS 2015 S essione 1.2 125