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In the Alboran domain, two crustal-thickening late-orogenic extension cycles are superposed. The importance of the late Alpine thinning of the Alpujarride-Sebtide crustal section on top of the Beni Bousera peridotites is discussed here in metamorphic petrological terms. The Alpine metamorphism operated first under a HP–LT gradient, and reached the eclogite facies in the Permian–Triassic phyllites, before retrogression under a high geothermal gradient. A contrasting, higher temperature metamorphism characterizes the pre-Permian section, reaching the HP-granulite facies at the bottom of the crustal section. By reference to the western European setting, the granulites relate to the Hercynian orogeny, as supported by the isotopic ages of the enclosed, armoured monazite crystals. Thus, thinning of an overthickened crust might have occurred there during the late Hercynian extension and Tethyan opening, before being reactivated during the late Oligocene. 相似文献
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Atmospheric forcing of the eastern tropical Pacific: A review 总被引:1,自引:8,他引:1
Jorge A. Amador Eric J. Alfaro Omar G. Lizano Victor O. Magaa 《Progress in Oceanography》2006,69(2-4):101
The increase in marine, land surface, atmospheric and satellite data during recent decades has led to an improved understanding of the air–sea interaction processes in the eastern tropical Pacific. This is also thanks to extensive diagnoses from conceptual and coupled ocean–atmosphere numerical models. In this paper, mean fields of atmospheric variables, such as incoming solar radiation, sea level pressure, winds, wind stress curl, precipitation, evaporation, and surface energy fluxes, are derived from global atmospheric data sets in order to examine the dominant features of the low level atmospheric circulations of the region. The seasonal march of the atmospheric circulations is presented to depict the role of radiative forcing on atmospheric perturbations, especially those dominating the atmosphere at low levels.In the tropics, the trade winds constitute an important north–south energy and moisture exchange mechanism (as part of the low level branch of the Hadley circulation), that determines to a large extent the precipitation distribution in the region, i.e., that associated with the Inter-Tropical Convergence Zone (ITCZ). Monsoonal circulations also play an important role in determining the warm season precipitation distribution over the eastern tropical Pacific through a large variety of air–sea–land interaction mechanisms. Westward traveling waves, tropical cyclones, low latitude cold air intrusions, and other synoptic and mesoscale perturbations associated with the ITCZ are also important elements that modulate the annual rainfall cycle. The low-level jets of the Gulf of California, the Intra-Americas Sea (Gulf of Mexico and Caribbean Sea) and Chocó, Colombia are prominent features of the eastern tropical Pacific low-level circulations related to sub-regional and regional scale precipitation patterns. Observations show that the Intra-Americas Low-Level Jet intensity varies with El Niño/Southern Oscillation (ENSO) phases, however its origin and role in the westward propagation and development of disturbances that may hit the eastern tropical Pacific, such as easterly waves and tropical cyclones, are still unclear. Changes in the intensity of the trade winds in the Caribbean Sea and the Gulf of Mexico (associated with eastern tropical Pacific wind jets) exert an important control on precipitation by means of wind–topography interactions. Gaps in the mountains of southern Mexico and Central America allow strong wind jets to pass over the continent imprinting a unique signal in sea surface temperatures and ocean dynamics of the eastern tropical Pacific.The warm pools of the Americas constitute an important source of moisture for the North American Monsoon System. The northeastern tropical Pacific is a region of intense cyclogenetic activity, just west of the coast of Mesoamerica. Over the oceanic regions, large-scale properties of key variables such as precipitation, moisture, surface energy fluxes and wind stress curl are still uncertain, which inhibits a more comprehensive view of the region and stresses the importance of regional field experiments. Progress has been substantial in the understanding of the ocean and atmospheric dynamics of the eastern tropical Pacific, however, recent observational evidence such as that of a shallow meridional circulation cell in that region, in contrast to the classic concept of the Hadley-type deep meridional circulation, suggests that more in situ observations to validate theories are still necessary.This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific Ocean. 相似文献
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Alberto Omar Vazquez-Hernandez Gilberto Bruno Ellwanger Luís Volnei Sudati Sagrilo 《Applied Ocean Research》2006,28(6):398-406
The characteristic environmental load effect for the design of mooring systems of floating units can be defined by means of three procedures: (a) the one associated to an extreme sea state with a given return period, (b) the worst one from a set of sea states on a contour line associated to a return period or (c) the extreme one based on response statistics for a long-term period. This work presents the result of a reliability-based partial safety factor calibration study for a LRFD mooring line design criteria considering the three approaches mentioned above. The calibration exercise is applied to three FPSOs considering North Sea environmental conditions and different water depths: 200, 800 and 3000 m. The mooring systems investigated take into account mooring lines made up of chains and polyester ropes. It is shown that, among all cases investigated, the design procedure based on the long-term response is the one that presents less scattered reliability indices around the target level. 相似文献
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Adnan A. Basma Samer A. Barakat Maher T. Omar 《Geotechnical and Geological Engineering》2003,21(3):225-242
The design methods currently used for earth reinforcement are mostly based on deterministic properties of both the soil and
the construction materials used. Nowadays, however, the general trend is designing at a specific degree of reliability. This
is even more true where the raw data such as soil properties exhibit significant variation. Deterministic solutions, in this
case, may not suffice. Therefore, this paper will attempt to use probabilistic formulations thereby modifying the existing
design procedure of reinforced earth retaining walls to account for uncertainties and variabilities. Through a first order
Taylor's series expansion about the mean, the mean and variance of the strip reinforcing components, namely width and length,
are derived in terms of the variations in the soil properties. Design charts that enable estimation of both mean and variance
are developed to avoid extensive partial differentiation involved in the computations. Using appropriate probability distributions
along with the mean and variance, the final design outputs are determined for a selected failure probability by introducing
what is refered to as 'risk index'. The results indicate that the risk index increases with an increase in the coefficient
of variations and a decrease in failure probability. Furthermore, it is shown that in some cases, depending on the variabilities
of the soil properties, the classical design technique produced a relatively high failure probability.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献