ABSTRACT
Recent global expansion of seismic data motivated a number of seismological studies of the Earth's inner core that proposed the existence of increasingly complex structure and anisotropy. In the meantime, new hypotheses of dynamic mechanisms have been put forward to interpret seismological results. Here, the nature of hemispherical dichotomy and anisotropy is re-investigated by bridging the observations of PKP(bc-df) differential travel-times with the iron bcc/hcp elastic properties computed from first-principles methods.The Candy Wrapper velocity model introduced here accounts for a dynamic picture of the inner core (i.e., the eastward drift of material), where different iron crystal shapes can be stabilized at the two hemispheres. We show that seismological data are best explained by a rather complicated, mosaic-like, structure of the inner core, where well-separated patches of different iron crystals compose the anisotropic western hemispherical region, and a conglomerate of almost indistinguishable iron phases builds-up the weakly anisotropic eastern side.
ABSTRACT
The distribution of epicenters and the focal mechanism of earthquakes are the basic tools in the determination of the regional stresses in a region. The Mediterranean basin is located at the plate boundary between the Eurasian and African plates. This boundary is of a complex nature and its dynamics is related to the opening of the Atlantic ocean and the closing of the Thetys sea. From Azores to Gibraltar the motion changes from strike-slip to reverse faulting under horizontal compression in NW-SE direction. From Gibraltar to the Caucasus, the boundary is complicated by the presence of secondary blocks, areas of extended deformation and subduction zones. The regional stresses show predominant horizontal compressions in a general NW-SE direction with some isolated areas of horizontal tensions in the Betics-Alboran sea, Apennines and north of the Hellenic arc
