GNGTS 2014 - Atti del 33° Convegno Nazionale

a value ever extremely little, except very near to the equator. Because we are not treating aeronomical problems (which have material motions tangential to the Earth’s surface) but we are mainly interested to radial displacements, the φ must be taken as the colatitude, and the value overcome the unity only near the poles. Then the Coriolis effects are dominant on other inertial forces, but our judgment should not be hasty about their real importance, because the existence of strong viscous friction can mitigate or make them negligible. Ekman number. In a fluid, the Ekman number is the ratio of the viscous forces to the Coriolis fictitious forces. It has different definitions but the classic one is Assuming for L and ω the same values as in the above discussed Rossby number, and for ν, the kinematic viscosity, the same value as in the preceding Reynold number, the resulting value is E k ≈10 9 which mean an inescapable prevalence of the viscous forces on the Coriolis fictitious forces. The trajectories that Coriolis force would impose (Figs. 1 and 2) in a non-viscous fluid (Paldor and Killworth, 1988) cannot be followed because the viscous friction. Then, in the mantle, at least for motions tangential to the sphere, the effects of the Earth’s rotation can be neglected. Round-trip or one-way tickets. There are at least three main version of the expanding Earth concept: i) The first version accepts the hypothesis of subduction and possibly of the convective flows (Owen, 1983, 1992; Perin, 2012). It is only a question of a non-equilibrium between the amount of subducted materials and new materials upwelled at the mid oceanic ridges – the last ones are hypothesized to prevail. ii) The more radical second version does not admit the existence of the subduction (Carey, 1975, 1976, 1996; Vogel, 1984; Maxlow, 2005). iii) A third version does not admit the existence of the large scale subduction, but a limited amount of regional underthrusts and overthrusts [few tens of km: Scalera (2007a, 2010, 2012)] is admitted, in agreement with geological observations. In plate tectonics the kinematics of the plates has been completed by a geodynamics that attributes the cause of continental drift to the convective cycles of the mantle and to other forces such as slab pull and slab-push. Instead, in the expansion global tectonics the main flows of the mantle materials are not necessarily moving along closed cycles of convection cells (Fig. 2a), but can be mainly extrusion flows along surfacewards paths. These non-cyclic surfaceward directed flows (one-way tickets instead of round-trips) must undergo the laws of the classical physics of fluid-dynamics. Being the Earth a rotating body, the inertial forces, like the Coriolis ones, must be present and, if sufficiently strong, should be considered among the factors influencing the final pattern of the flows. In an expanding Earth, at least in the upper mantle, the radial flows of mantle materials are not necessarily slowed by viscous resistances. As explained in other papers (Scalera, 2003, 2010, 2012) the expansion can favor the isostatic rising of very deep material along huge and deep geofractures, which morphology – revealed by catalogues of relocated hypocenters (Engdahl et al. , 1998) – resembles trees or smoke plumes enlarging and assuming the shape of great calderas (like the south Tyrrhenian one) towards the surface. Sudden motion, in the upper mantle, is revealed by earthquakes. The isostatic rising of these materials can nullify the rising of deep materials due to thermal convection, in the sense that the progressive enlarging size – triggered and driven by global expansion – of the ‘room’ in which the rising materials are moving may not allow the onset of the convective circulation. In this room the velocity of rising is not constant but irregular and mainly impulsive, the rising episodes coinciding with changing of phase, and its range 178 GNGTS 2014 S essione 1.2