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Antonis Polatidis Anastasia Kiratzi Panagiotis Hatzidimitriou Basil Margaris 《Tectonophysics》2003,367(1-2):29-40
Qβ for shear-waves is determined for the inner part of the Hellenic arc, the back-arc area, as a function of frequency in the range 0.6–16 Hz. We used 314 digital records from 32 earthquakes with magnitudes (Mw) ranging from 3.9 to 5.1. Epicentral distances ranged from 65 to 515 km. The data were obtained in 1997 during a 6-month operation of a digital portable network in Greece. The Qβ estimates were made for five frequency bands centred at 0.8, 1.5, 3.0, 6.0 and 12.0 Hz and the Qβ values obtained were 47, 79, 143, 271 and 553, respectively. The results show that Qβ for S-waves increases with frequency taking the form Qβ=55f 0.91 (or Qβ−10.018f−0.91). The high attenuation and the strong frequency dependence found, which is close to the frequency dependence of coda Q for Greece, are characteristic of an area with high seismicity, rapid extension, and in agreement with other similar studies in Greece. 相似文献
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Antonis D. Pinotsis 《Celestial Mechanics and Dynamical Astronomy》2010,108(2):187-202
We studied systematically cases of the families of non-symmetric periodic orbits in the planar restricted three-body problem.
We took interesting information about the evolution, stability and termination of bifurcating families of various multiplicities.
We found that the main families of simple non-symmetric periodic orbits present a similar dynamical structure and bifurcation
pattern. As the Jacobi constant changes each branch of the characteristic of a main family spirals around a focal point-terminating
point in x- at which the Jacobi constant is C
∞ = 3 and their periodic orbits terminate at the corotation (at the Lagrangian point L4 or L5). As the family approaches asymptotically its termination point infinite changes of stability to instability and vice versa
occur along its characteristic. Thus, infinite bifurcation points appear and each one of them produces infinite inverse Feigenbaum
sequences. That is, every bifurcating family of a Feigenbaum sequence produces the same phenomenon and so on. Therefore, infinite
spiral characteristics appear and each one of them generates infinite new inner spirals and so on. Each member of these infinite
sets of the spirals reproduces a basic bifurcation pattern. Therefore, we have in general large unstable regions that generate
large chaotic regions near the corotation points L4, L5, which are unstable. As C varies along the spiral characteristic of every bifurcating family, which approaches its focal
point, infinite loops, one inside the other, surrounding the unstable triangular points L4 or L5 are formed on their orbits. So, each terminating point corresponds to an asymptotic non-symmetric periodic orbit that spirals
into the corotation points L4, L5 with infinite period. This is a new mechanism that produces very large degree of stochasticity. These conclusions help us
to comprehend better the motions around the points L4 and L5 of Lagrange. 相似文献
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Hamdan Hamdan Nikos Andronikidis George Kritikakis Nikos Economou Zacharias Agioutantis Paul Schilizzi Chrysanthos Steiakakis Christodoulos Papageorgiou Panagiotis Tsourlos George Vargemezis Antonis Vafidis 《Environmental Earth Sciences》2014,72(5):1589-1598
In this paper, the application of 2D and 3D electrical resistivity methods in geotechnical investigations is explored through a case study in Northern Greece. These two methods were employed at a lignite surface mining operation where fracture zones and discontinuities have been recently observed close to the pit boundaries. The main aim of the geophysical survey was to estimate the inclination of the contact between the Neogene and Schist/Carbonate formations near the southern limits of the pit, as well as to estimate the thickness of the carbonate rocks on top of the Schist formations to evaluate the stability of the southern slopes. Synthetic data were initially generated to help plan an efficient electrical tomography survey, in a region with complex geology and irregular terrain. Three configurations (Wenner–Schlumberger and dipole–dipole or pole–dipole) proved essential in such conditions and helped improving the resolution of the resistivity section. The sections were then calibrated by boreholes. Finally, the geophysical survey provided invaluable data regarding the geometry of the bedrock and possible faults, which was essential for the slope stability calculations. 相似文献
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Diego Perugini Giampiero Poli George Christofides George Eleftheriadis Antonis Koroneos Triantafyllos Soldatos 《Geological Journal》2004,39(1):63-80
Two distinct groups of subduction‐related (orogenic) granitoid rocks, one Jurassic and the other Tertiary, occur in the area between the Vardar (Axios) Zone and the Rhodope Massif in northern Greece. The two groups of granitoids differ in many respects. The first group shows evolved geochemical characters, it is not associated with mafic facies, and evidence of magmatic interaction between mantle‐ and crustal‐derived melts is lacking. The second group has less evolved geochemical characters, it is associated with larger amount of mafic facies, and magmatic interaction processes between mantle‐derived and crustal melts are ubiquitous as evidenced by mafic microgranular enclaves and synplutonic dykes showing different enrichment in K2O, Ti, and incompatible elements. This kind of magmatism can be attributed to the complex geodynamic evolution of the area. In particular, we suggest that two successive subduction events related to the closure of the Vardar and the Pindos oceans, respectively, occurred in the investigated area from Late Jurassic to Tertiary. We relate the genesis of Jurassic granitoids to the first subduction event, whereas Tertiary granitoids are associated with the second subduction. Fluids released by the two subducted slabs induced metasomatic processes generating a ‘leopard skin’ mantle wedge able to produce mafic melts ranging from typical calc‐alkaline to ultra‐potassic. Such melts interacted in various amounts with crustal calc‐alkaline anatectic melts to generate the wide spectrum of Tertiary granitoids occurring in the study area. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献