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101.
Yehuda Gradus 《Geoforum》1977,8(1):29-32
The cargo movement over the continental bridge annually since 1970 is shown in Table 2. These figures should be compared with the (dry) volume of trade via Eilat annually (see third column of the same table) and they include the traffic via the continental bridge. From this table it is clear that the amount of cargo in transit over the bridge was not a major component of the total traffic through Eilat. 相似文献
102.
103.
A receiver function study across the Dead Sea Transform 总被引:4,自引:0,他引:4
104.
Marian Anghel Yehuda Ben-Zion Ramiro Rico-Martinez 《Pure and Applied Geophysics》2004,161(9-10):2023-2051
— We present a method of constructing low-dimensional nonlinear models describing the main dynamical features of a discrete 2-D cellular fault zone, with many degrees of freedom, embedded in a 3-D elastic solid. A given fault system is characterized by a set of parameters that describe the dynamics, rheology, property disorder, and fault geometry. Depending on the location in the system parameter space, we show that the coarse dynamics of the fault can be confined to an attractor whose dimension is significantly smaller than the space in which the dynamics takes place. Our strategy of system reduction is to search for a few coherent structures that dominate the dynamics and to capture the interaction between these coherent structures. The identification of the basic interacting structures is obtained by applying the Proper Orthogonal Decomposition (POD) to the surface deformation fields that accompany strike-slip faulting accumulated over equal time intervals. We use a feed-forward artificial neural network (ANN) architecture for the identification of the system dynamics projected onto the subspace (model space) spanned by the most energetic coherent structures. The ANN is trained using a standard back-propagation algorithm to predict (map) the values of the observed model state at a future time, given the observed model state at the present time. This ANN provides an approximate, large-scale, dynamical model for the fault. The map can be evaluated once to provide a short-term predictions or iterated to obtain a prediction for the long-term fault dynamics. 相似文献
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106.
Christian Hensen Marianne Nuzzo Luis M. Pinheiro Barbara Bock Warner Brückmann 《Geochimica et cosmochimica acta》2007,71(5):1232-1248
Mud volcanism in the Gulf of Cadiz occurs over a large area extending from the shelf to more than 3500 m water depth and is triggered by compressional stress along the European-African plate boundary, affecting a deeply faulted sedimentary sequence of locally more than 5 km thickness. The investigation of six active sites shows that mud volcano (MV) fluids, on average, are highly enriched in CH4, Li, B, and Sr and depleted in Mg, K, and Br. The purity of the fluids is largely controlled by the intensity of upward directed flow. Flow rates could be constrained by numerical modelling and vary between <0.05 and 15 cm yr−1. Application of δD-δ18O systematics identifies clay mineral dehydration, most likely within Mesozoic and Tertiary shales and marls, as the major source of fluids. Hence, Cl and Na in the pore fluids are mostly depleted below seawater values, following a general trend of dilution. However, deviations from this trend occur and are likely caused by the dissolution of halite in evaporitic deposits. Other secondary processes overprinting the original fluid composition may occur along the flow path, such as dissolution of anhydrite or gypsum and/or the formation of calcite and dolomite. Different sources of fluids are also indicated by variations in 87Sr/86Sr, which range from 0.7086 to 0.7099 at the different sites. Dehydration may be induced primarily by overburden and tectonic compression; however, very high concentrations of Li and B, specifically at Captain Arutyunov MV (CAMV) indicate additional leaching at temperatures above 150 °C, which could be explained by the injection of hot fluids along deep penetrating, major E-W strike-slip fault systems. This hypothesis is supported by the occurrence of generally thermogenic, but significantly CH4-enriched, light volatile hydrocarbon gases at CAMV which cannot be explained by shallow microbial methanogenesis. Li and Li/B ratios from different types of hot and cold vents are used to infer that high temperature signals seem to be preserved at various cold vent locations and indicate a closer coupling of both systems in continental margin environments than outlined in previous studies. 相似文献
107.
A habitat assessment of 1,707 km of rivers in the Federal State of Brandenburg, Germany, was undertaken using the desk-based ‘overview method’. This method includes the analysis of different sources such as topographic and thematic maps, reports, remote sensing data, and interviews with authorities. It compares actual habitat conditions with natural conditions, and assesses the human disturbances using a seven-step scale. Results show, that in Brandenburg more than 50% of surveyed river units are heavily (class 5) to totally disturbed (class 7) and only slightly more than 20% are undisturbed (class 1) to little disturbed (class 2). Main human disturbances are canalization, bank stabilizations, flood control, migration barriers, and agricultural and urban development in the floodplain. All survey data and maps are embedded in a geographical information system (GIS) that not only allows future analysis and use in river restoration management by experts, but also serves as information for the public. The river habitat map of Brandenburg is part of the river habitat map of the entire Germany. 相似文献
108.
Evolution and degradation of flat‐top mesas in the hyper‐arid Negev,Israel revealed from 10Be cosmogenic nuclides 下载免费PDF全文
Ronen Boroda Ari Matmon Rivka Amit Itai Haviv Maurice Arnold Georges Aumaître Didier L. Bourlès Karim Keddadouche Yehuda Eyal Yehouda Enzel 《地球表面变化过程与地形》2014,39(12):1611-1621
Mesas are ubiquitous landforms in arid and semiarid regions and are often characterized by horizontal stratified erodible rocks capped by more resistant strata. The accepted conceptual model for mesa evolution and degradation considers reduction in the width of the mesa flat‐top plateau due to cliff retreat but ignores possible denudation of the mesa flat‐top and the rates and mechanism of erosion. In this study we examine mesas in the northeastern hyperarid Negev Desert where they appear in various sizes and morphologies and represent different stages of mesa evolution. The variety of mesas within a single climatic zone allows examination of the process of mesa evolution through time. Two of the four sites examined are characterized by a relatively wide (200–230 m) flat‐top and a thick caprock whereas the other two are characterized by a much narrower remnant flat‐top (several meters) and thinner caprock. We use the concentration of the cosmogenic nuclide 10Be for: (a) determining the chronology of the various geomorphic features associated with the mesa; and (b) understanding geomorphic processes forming the mesa. The 10Be data, combined with field observations, suggest a correlation between the width of flat‐top mesa and the denudation and cliff retreat rates. Our results demonstrate that: (a) cliff retreat rates decrease with decreasing width of the flat‐top mesa; (b) vertical denudation rates increase with decreasing width of the flat‐top mesa below a critical value (~60 m, for the Negev Desert); (c) the reduction in the width of the flat‐top mesa is driven mainly by cliff retreat accompanied by extremely slow vertical denudation rate which can persist for a very long time (>106 Ma); and (d) when the width of the mesa decreases below a certain threshold, its rate of denudation increases dramatically and mesa degradation is completed in a short time. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
109.
U/Th systematics and ages of authigenic carbonates from Hydrate Ridge, Cascadia Margin: recorders of fluid flow variations 总被引:6,自引:0,他引:6
B.M.A. Teichert A. Eisenhauer G. Bohrmann B. Bock 《Geochimica et cosmochimica acta》2003,67(20):3845-3857
Uranium (U) concentrations and activity ratios (δ234U) of authigenic carbonates are sensitive recorders of different fluid compositions at submarine seeps of hydrocarbon-rich fluids (“cold seeps”) at Hydrate Ridge, off the coast of Oregon, USA. The low U concentrations (mean: 1.3 ± 0.4 μg/g) and high δ234U values (165-317‰) of gas hydrate carbonates reflect the influence of sedimentary pore water indicating that these carbonates were formed under reducing conditions below or at the seafloor. Their 230Th/234U ages span a time interval from 0.8 to 6.4 ka and cluster around 1.2 and 4.7 ka. In contrast, chemoherm carbonates precipitate from marine bottom water marked by relatively high U concentrations (mean: 5.2 ± 0.8 μg/g) and a mean δ234U ratio of 166 ± 3‰. Their U isotopes reflect the δ234U ratios of the bottom water being enriched in 234U relative to normal seawater. Simple mass balance calculations based on U concentrations and their corresponding δ234U ratios reveal a contribution of about 11% of sedimentary pore water to the bottom water. From the U pore water flux and the reconstructed U pore water concentration a mean flow rate of about 147 ± 68 cm/a can be estimated. 230Th/234U ages of chemoherm carbonates range from 7.3 to 267.6 ka. 230Th/234U ages of two chemoherms (Alvin and SE-Knoll chemoherm) correspond to time intervals of low sealevel stands in marine isotope stages (MIS) 2, 4, 5, 6, 7 and 8. This observation indicates that fluid flow at cold seep sites sensitively reflects pressure changes of the hydraulic head in the sediments. The δ18OPDB ratios of the chemoherm carbonates support the hypothesis of precipitation during glacial times. Deviations of the chemoherm δ18O values from the marine δ18O record can be interpreted as to reflect temporally and spatially varying bottom water and/or vent fluid temperatures during carbonate precipitation between 2.6 and 8.6°C. 相似文献
110.