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41.
Relationships between the surface area and age of alluvial deposits were used to estimate the residence time of alluvium in the 2205 km2 Waipaoa River basin, New Zealand. The contemporary Waipaoa River is an efficient transporter of sediment to the continental shelf, but the basin has been characterized by rapid channel and valley aggradation in the historic period, and by extensive mid‐ to late Holocene alluvial storage in the lower reaches. The area‐weighted mean age of alluvial deposits in the lower part of the river basin is ~4400 yr. These deposits comprise terrace remnants isolated by downcutting, and Holocene to Recent sediments that are potentially remobilizable by the modern river. Even though the amount of storage is small relative to downstream transport, the majority of the potentially remobilizable alluvium is likely to remain in storage for >100 yr, and its half‐life (time for 50 per cent removal) is >2000 yr. Within the confines of the flfloodplain, the apparent ‘loss’ of older deposits is due primarily to burial, but losses of the most recent deposits are due almost entirely to remobilization (30–40 per cent), with the remainder preserved in the alluvial record for at least 104 yr. Most of this sediment is likely to remain in storage until there is a shift to a degradational state. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
42.
Research of several years has confirmed the general aspect that the most acceptable model in quasars' nuclei is a rotating Kerr black hole.Assuming the Kerr type potential given by the equation:
相似文献
43.
Environmental impact assessment using FORM and groundwater system reliability concept: case study Jining, China 总被引:2,自引:0,他引:2
In this paper, fist-order reliability method (FORM) is used to evaluate the impacts of uncertainties posed by traditional
deterministic models on the environment in Jining, China. Because of groundwater contamination in shallow aquifer, and an
increase in water demand, the new wells target the confined aquifer with constant pumping rate of 5,000 m3/d. Using Theis equation, the groundwater drawdown is analyzed to determine whether the confined aquifer will be contaminated.
Although the piezometric level is higher than the phreatic level by 11.0 m, the risk of drawdown is still 19.49% when the
pumping rate of 5,000 m3/d is maintained for 2 years. The deterministic model indicates a drawdown of 8.94 m which is lower than the maximum tolerance
drawdown of 11.0 m. The sensitivity and uncertainty analysis reveal that the model result is more sensitive to transmissivity
than specific yield, while the reliability analysis offers significant information for the decision makers. This approach
exposes and minimizes the risk of undesirable consequences such as groundwater contamination. 相似文献
44.
The annual rainfall data of Athens rain gauge stations, for the last 119 years, is compared with the occurrence of large (M 6) earthquakes along the fault and thrust systems in the vicinity of Athens and interesting correlations have been observed.This preliminary investigation reveals the possible occurrence of a large earthquake in the region of Athens till 1993. 相似文献
45.
Effect of torsional stiffness of prestressed concrete box girders and uplift of abutment bearings on seismic performance of bridges 总被引:1,自引:1,他引:0
Christos P. Katsaras Telemachos B. Panagiotakos Basil Kolias 《Bulletin of Earthquake Engineering》2009,7(2):363-375
Uplift of certain abutment bearings during earthquake may be utilized as a safety mechanism for the protection of the bridge
against excessive stress. For this reason design codes such as Eurocode 8 permit the uplift of such bearings under certain
conditions. Uplift of an abutment bearing occurs when the torque at the deck end exceeds a critical value. Therefore the torsional
stiffness of the deck, before or after concrete cracking, is an important factor. In this work realistic values for the cracked
torsional stiffness of the bridge deck are estimated from a parametric study of typical thin-walled prestressed box girders,
based on non-linear analysis of softened space truss models proposed in the literature. Moreover the interaction between bearing
uplift and pier flexural response is investigated and recommendations for the seismic design of bridges are proposed, taking
into account the possibility of uplift of abutment bearings before or after yielding of the piers. 相似文献
46.
Ch. Kkallas C. B. Papazachos D. Boore Ch. Ventouzi B. N. Margaris 《Bulletin of Earthquake Engineering》2018,16(11):5121-5150
We model the macroseismic damage distribution of four important intermediate-depth earthquakes of the southern Aegean Sea subduction zone, namely the destructive 1926 M?=?7.7 Rhodes and 1935 M?=?6.9 Crete earthquakes, the unique 1956 M?=?6.9 Amorgos aftershock (recently proposed to be triggered by a shallow event), and the more recent 2002 M?=?5.9 Milos earthquake, which all exhibit spatially anomalous macroseismic patterns. Macroseismic data for these events are collected from published macroseismic databases and compared with the spatial distribution of seismic motions obtained from stochastic simulation, converted to macroseismic intensity (Modified Mercalli scale, IMM). For this conversion, we present an updated correlation between macroseismic intensities and peak measures of seismic motions (PGA and PGV) for the intermediate-depth earthquakes of the southern Aegean Sea. Input model parameters for the simulations, such as fault dimensions, stress parameters, and attenuation parameters (e.g. back-arc/along anelastic attenuation) are adopted from previous work performed in the area. Site-effects on the observed seismic motions are approximated using generic transfer functions proposed for the broader Aegean Sea area on the basis of VS30 values from topographic slope proxies. The results are in very good agreement with the observed anomalous damage patterns, for which the largest intensities are often observed at distances >?100 km from the earthquake epicenters. We also consider two additional “prediction” but realistic intermediate-depth earthquake scenarios, and model their macroseismic distributions, to assess their expected damage impact in the broader southern Aegean area. The results suggest that intermediate-depth events, especially north of central Crete, have a prominent effect on a wide area of the outer Hellenic arc, with a very important impact on modern urban centers along northern Crete coasts (e.g. city of Heraklion), in excellent agreement with the available historical information. 相似文献
47.
Lionel Carter Barbara Manighetti Mike Elliot Noel Trustrum Basil Gomez 《Global and Planetary Change》2002,33(3-4)
The last post-glacial transgression and present highstand of sea level were accompanied by a reduction in the terrigenous flux to the deep ocean bordering the active convergent margin off the eastern North Island of New Zealand. Although in accord with long-established models of highstand shelf deposition, new data from giant piston core MD97 2121 (2314 m depth) reveal that the flux also varied with terrigenous supply and palaeocirculation. Between 15 and 9.5 ka, the flux reduced from 33 to 20 g/cm2/ka as supply declined with an expanding vegetation cover, and mud depocentres became established on the continental shelf. An increase from 20 to 27 g/cm2/ka during 9.5–3.5 ka coincided with a strengthened East Cape Current which probably introduced sediment from fluvial and shelf sources in the north. The flux profile shows no immediate response to the establishment of modern sea level 7 ka. However, accumulation decreased from 3.5 to 1 ka as more sediments were retained on the shelf, possibly under wind-strengthened, along-shelf currents. Over the last 1 ka, the flux decline halted under increased terrigenous supply during anthropogenic development of the land.Despite the proximity of the North Island's Central Volcanic Region, major eruptions caused only brief increases (centuries duration) in the terrigenous flux through direct deposition of airfall and possibly fluvial redistribution of onshore volcanic deposits. Frequent earthquakes also had little short-term effect on accumulation although such events, along with volcanism, probably contribute to the long-term high flux of the region.The other measured flux component, biogenic carbonate, reached maxima of 6 g/cm2/ka between 11 and 8.5 ka when nutrient-bearing waters of the East Cape Current dominated the palaeoceanography. After these peaks, carbonate accumulation declined gradually to modern levels of 3 g/cm2/ka. 相似文献
48.
49.
The relationship between monsoon cloud cover and incoming solar radiation in the Arabian Sea is examined utilising the available observations of daily mean total cloud amount and solar radiation collected during the summer monsoon. With these data sets, various cloud correction formulae are evaluated. For the estimation of solar radiation, the formulation of Laevastu (1960) is best, with a minimum error of -4%. A multiple polynomial regression equation based on cloud cover and noon altitude of the sun is developed for estimation of daily radiation. The error between estimated and observed radiation is -2%. 相似文献
50.
The hydrography and circulation pattern off Antarctica in the Indian Ocean region are studied using vertical sections of temperature, salinity and oxyty approximately along 20°E, 77°E and 90°E, and the dynamic topography of the sea surface with reference to 1000 db. Based on the oceanographic characteristics, the whole region under study can be divided into three zones, the extreme ends being characterised by the frontal structure. The dicothermal layer is conspicuous during summer south of 50°S. The surface flow around Antarctica is mainly zonal. The East Wind Drift, found as a narrow westward flow near Antarctica, is observed at a lower latitude in the eastern Indian Ocean where the land extends northword. Contrary to expectation there is evidence of a westward flowing surface current at about 35°S between 45°E and 65°E. 相似文献
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