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141.
Kinematics of the Iberia–Maghreb plate contact from seismic moment tensors and GPS observations 总被引:2,自引:0,他引:2
Daniel Stich Enrico Serpelloni Flor de Lis Mancilla Jose Morales 《Tectonophysics》2006,426(3-4):295-317
The Iberian Peninsula and the Maghreb experience moderate earthquake activity and oblique, NW–SE convergence between Africa and Eurasia at a rate of 5 mm/yr. Coeval extension in the Alboran Basin and a N35°E trending band of active, left-lateral shear deformation in the Alboran–Betic region are not straightforward to understand in the context of regional shortening, and evidence complexity of deformation at the plate contact. We estimate 86 seismic moment tensors (MW 3.3 to 6.9) from time domain inversion of near-regional waveforms in an intermediate period band. Those and previous moment tensors are used to describe regional faulting style and calculate average stress tensors. The solutions associated to the Trans-Alboran shear zone show predominantly strike-slip faulting, and indicate a clockwise rotation of the largest principal stress orientation compared to the regional convergence direction (σ1 at N350°E). At the N-Algerian and SW-Iberian margins, reverse faulting solutions dominate, corresponding to N350°E and N310°E compression, respectively. Over most of the Betic range and intraplate Iberia, we observe predominately normal faulting, and WSW–ENE extension (σ3 at N240°E). From GPS observations we estimate that more than 3 mm/yr of African (Nubian)–Eurasian plate convergence are currently accommodated at the N-Algerian margin, 2 mm/yr in the Moroccan Atlas, and 2 mm/yr at the SW-Iberian margin. 2 mm/yr is a reasonable estimate for convergence within the Alboran region, while Alboran extension can be quantified as 2.5 mm/yr along the stretching direction (N240°E). Superposition of both motions explains the observed left-lateral transtensional regime in the Trans-Alboran shear zone. Two potential driving mechanisms of differential motion of the Alboran–Betic–Gibraltar domain may coexist in the region: a secondary stress source other than plate convergence, related to regional-scale dynamic processes in the upper mantle of the Alboran region, as well as drag from the continental-scale motion of the Nubian plate along the southern limit of the region. In the Atlantic Ocean, the 3.5 mm/yr, westward motion of the Gibraltar Arc relative to intraplate Iberia can be accommodated at the transpressive SW-Iberian margin, while available GPS observations do not support an active subduction process in this area. 相似文献
142.
Giuseppe Altavilla Maria Teresa Botticella Enrico Cappellaro Massimo Turatto 《Astrophysics and Space Science》2012,341(1):163-178
Despite decades of dedicated efforts there are still basic questions to answer with regard to Supernova progenitor systems and explosion mechanisms. In particular, in the last years a number of exceptionally bright objects and extremely faint events have demonstrated an unexpected large Supernova variety. 相似文献
143.
Luciano Morselli Elena Bernardi Ivano Vassura Fabrizio Passarini Enrico Tesini 《Journal of Atmospheric Chemistry》2008,59(3):151-170
The results of a 8 year survey of wet and dry depositions collected in Bologna (Northern Italy) are presented and discussed:
monthly fluxes of the main ions (hydrogen, sodium, potassium, calcium, magnesium, ammoniacal and nitrate nitrogen, sulphate
and chloride) have been registered and statistically discussed. The trend of hydrogen ion, whose largest correlation in the
global deposition was found with sulphate, is clearly downwards, with peaks mainly in winter months. By means of a data factor
analysis, three main sources to explain the variability of the deposition chemistry were recognized: an anthropogenic contribution
(particularly represented by NO3
−, SO4
2−, H+), the sea spray (Na+, Cl− and, to a lesser extent, K+ and Mg2+) and a terrigenous fraction, particularly characterized by higher Ca2+ concentration; however, some concentration peaks of this ion have been found in association with some episodes of Saharan
dust transportation. 相似文献
144.
Luca Gasperini Enrico Bonatti Sonia Albertazzi Luisa Forlani Carla A. Accorsi Giuseppe Longo Mariangela Ravaioli Francesca Alvisi Alina Polonia Fabio Sacchetti 《地学学报》2009,21(6):489-494
Cheko, a small lake located in Siberia close to the epicentre of the 1908 Tunguska explosion, might fill a crater left by the impact of a fragment of a Cosmic Body. Sediment cores from the lake’s bottom were studied to support or reject this hypothesis. A 175‐cm long core, collected near the center of the lake, consists of an upper ~1 m thick sequence of lacustrine deposits overlaying coarser chaotic material. 210Pb and 137Cs indicate that the transition from lower to upper sequence occurred close to the time of the Tunguska Event. Pollen analysis reveals that remains of aquatic plants are abundant in the top post‐1908 sequence, but are absent in the lower pre‐1908 portion of the core. These results, including organic C, N and δ13C data, suggest that Lake Cheko formed at the time of the Tunguska Event. 相似文献
145.
Stefano Bianchi Marco Chiaberge Enrico Piconcelli Matteo Guainazzi Giorgio Matt 《Monthly notices of the Royal Astronomical Society》2008,386(1):105-110
We analyse Chandra , XMM–Newton and Hubble Space Telescope ( HST ) data of the double-nucleus Ultraluminous Infrared Galaxy (ULIRG), Mrk 463. The Chandra detection of two luminous ( L 2–10 keV = 1.5 × 1043 and 3.8 × 1042 erg cm−2 s−1 ) , unresolved nuclei in Mrk 463 indicates that this galaxy hosts a binary active galactic nucleus (AGN), with a projected separation of ≃3.8 kpc ( 3.83 ± 0.01 arcsec). While the East nucleus was already known to be a type 2 Seyfert (and this is further confirmed by our Chandra detection of a neutral iron line), this is the first unambiguous evidence in favour of the AGN nature of the West nucleus. Mrk 463 is therefore the clearest case so far for a binary AGN, after NGC 6240. 相似文献
146.
The paper illustrates an approach for implementing the Precautionary Principle in risk management, exemplified by a procedure
aimed at choosing the height of a rockfall barrier protecting a railway stretch. Risk is expressed by the frequency f of blocks hitting the railway—i.e. by the ratio between the number of blocks reaching the railway and the number of blocks
falling from the slope—assessed through software simulation of the falling of the blocks. The height from which a block may
fall is considered to be the main uncertainty factor in risk estimation, which translates into uncertainty as to the level
of risk, as every simulation shows that more than one impact frequency is possible. Such uncertainty justifies the precautionary
approach to the design of the barrier, and is represented mathematically by means of possibility and probability distribution
functions. The distributions make it possible to express the degree of precaution related to a barrier as the level of confidence,
in terms of necessity or probability measures—that can be placed on the fact that, because of the barrier, the impact frequency,
although uncertain, will not exceed what is acceptable. It will be shown that the degree of precaution takes quite different
values if possibility theory is used instead of probability theory. Finally some simple cost/benefit analyses, that explicitly
and quantitatively consider the degree of precaution, are exemplified. 相似文献
147.
Enrico Ferrero Luca Mortarini Massimigliano Manfrin Arnaldo Longhetto Rita Genovese Renato Forza 《Boundary-Layer Meteorology》2009,130(3):347-363
Boundary-layer instabilities are studied by analyzing the results of laboratory simulations of wall turbulence in a shear-driven
rotating flow. The experiments were carried out in the Turin University Laboratory rotating water tank, where a circular flow
was generated by either increasing (spin-up) or decreasing (spin-down) the rotation speed of the platform. The flow was measured
using a Particle Image Velocimetry technique and the developed turbulence analyzed. Two cases were accounted for, in the former
the measurements were performed over a smooth surface (bottom of the tank), while in the latter a rough-to-smooth transition
was considered. The turbulent boundary layer developed inside the tank is analyzed by means of vertical profiles of mean and
turbulent quantities and on the basis of drag coefficients. Then turbulent structures developed in the different cases are
shown and discussed in terms of the vorticity fields. Finally, an analysis based on the concept of swirling strength was carried
out to select among the vortex extremes those associated with a coherent structure. 相似文献
148.
149.
Enrico Bonatti 《Earth and Planetary Science Letters》1978,37(3):369-379
Anomalous topographic highs are found along many large oceanic fracture zones, frequently in the form of transverse ridges elongated parallel to the fractures both within and outside of the transform zone. These crustal highs are one or more kilometers shallower than the adjacent “normal” crust of equivalent age. Their elevation is frequently higher than the axial zone of lithospheric accretion. Geophysical and petrological data from the Vema, St. Paul, Romanche (Atlantic Ocean), Owen (Indian Ocean), Alula (Gulf of Aden), and other fracture zones suggest that the anomalous transverse ridges are not the result of excess volcanism, but rather of tectonic uplift of upper mantle and crustal blocks.Factors which may determine vertical tectonism along fracture zones include: (1) horizontal thermal conduction across a fracture zone from a lithospheric accreting segment; (2) viscodynamic forces operating in a fracture zone close to its intersection with an accreting segment; and (3) compressional and tensional horizontal stresses operating along a fracture zone, and created by several causes, the major one being small changes in the direction of spreading. Among these various factors, compressional and tensional horizontal stresses are probably the main cause of vertical tectonism in fracture zones. During the vertical motion of upper mantle/crustal blocks, ultramafic rocks, due to their physical properties, are uplifted preferentially.One of the implications of fracture zone vertical tectonism is that the age/depth of the crust relationship may not apply in regions with large fracture zones. In one well-documented case, a transverse crustal block at the Romanche fracture zone subsided during the last 5 m.y. at an average rate more than one order of magnitude faster than crust of equivalent age. 相似文献
150.