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The Central Apennines, Italy, are characterized by moderate seismic activity on normal faults, oriented in directions parallel to the Apenninic chain. The subject of this study is the Umbria-Marche Apennines, a segment approximately 200-km long, where three main seismic events occurred in the last three decades. The 1979 Norcia earthquake was a Mw = 5.8 event, taking place at the south end of the considered segment. The 1984 Gubbio earthquake was a Mw = 5.6 event which took place at the north end. The 1997-1998 Colfiorito sequence constituted 8 main shocks with magnitudes Mw between 5 and 6 and epicenters located between the Gubbio and the Norcia earthquake areas. A model made of an elastic half-space is considered, in which the seismic sources are represented by rectangular dislocations which have the appropriate values of source parameters, and in which the static stress field produced by each event is calculated. The analysis of the Coulomb stress change as a function of time shows that the coseismic stress transfer and fault interaction played an important role in the region during the past three decades: 7 earthquakes of the 9 considered took place where then stress change is positive. Such an interaction has been confirmed by the analysis of the aftershocks in the Colfiorito zone post September 26, 1997: about the 61% of the aftershocks considered took place where the stress change is positive. The comparison between the Coulomb stress change due to the coseismic stress transfer and the rate of change due to the tectonic stress allows us to quantify the time advance of the earthquakes. The pattern of coseismic Coulomb stress change shows positive values in two areas that can be regarded as historical seismic gaps.

It has been known for many years that waves of different kind propagating in a fluid and incident on a mean flow localized shear layer can exhibit, in the linear theory, a reflection coefficient larger than unity. When this phenomenon takes place the wave is said to be over-reflected at the shear layer. In this paper the over-reflection of inertial-gravity waves in a stratified rotating fluid in horizontal sheared motion is studied by making use of the constancy of the net vertical energy flux associated with the wave field. It is found that over-reflection can take place if some physical conditions, explicitly evaluated, are locally satisfied in the fluid. Such conditions are discussed and a comparison is carried out with the same phenomenon in a nonrotating system.

The non-linear interaction between large-scale Rossby waves is considered making use of a spectral model of a barotropic atmosphere in spherical geometry. It is found that, if an arbitrary number of zonal components is taken into account it is possible to predict the non-linear energy and enstrophy flux between Rossby waves whose interaction cannot be predicted by single triadic resonance. It is shown, referring to the results of a paper by Baines, that such kind of, zonally mediated, non-linear energy flux is capable of explaining some relevant features of numerical integrations of truncated models with a large number of components and, could, as a consequence be responsible of some features of the large-scale circulation.