A study of world stratigraphy reveals, somewhat unexpectedly, that there were extensive basalt flows in the early Precambrian, but the Upper Precambrian and the whole of the Palaeozoic Era, with some insignificant exceptions, are practically devoid of flood basalts. In fact there were very few cruptions between about 1000 M.yr. and about 200 M.yr, ago. Since Upper Triassic time, however, basalt floods have come to cover very extensive areas in both the hemispheres, and the activity is continuing almost unabated. Recent researches on the origin and nature of the mid-ocean ridges have indicated that the flood basalts are apparently genetically connected with these ridges which appear to have begun to open the present oceans within the past 150 M.yr. Basalts occur on the opposite coasts where the continents were formerly together, for example, Peninsular India and Eastern Africa. However, along certain coastal areas there are no basalts of appropriate age even though a mid-ocean ridge exists beyond these. This is true, for example, of eastern North America and western Europe. Elsewhere neither basalt flows nor a mid-oceanic ridge exist where the continents are reasonably believed to have been together. These anomalies call for an explanation, and it is suggested that the observed features can be explained by the fact that two distinct phenomena, crustal sliding and global expansion, have been responsible for the present disposition of the continents. The net result of these two activities has been recognised as ‘Continental Drift’. 相似文献
The geologic structures associated with several selected dam sites in Jordan and the tectonic effects on dam foundations and reservoir margins are reviewed. Rock defects, especially discontinuities represented by faults and closely spaced, open joints are investigated. Related problems, such as loss of water from the reservoir by seepage and leakage within the dam foundation are evaluated. The regional seismicity is analyzed and a design earthquake is established for each dam site.
Two major embankment dams are investigated, together with two large proposed dams and several small dams.
This paper discusses in some detail the regional setting and site-specific geology, and the occurrence, size and inclination of faults and joints at each dam site. Moreover, the effects of the faults on the operational performance of each dam are described and specific techniques are used or proposed for remediation are outlined.
The study shows that the combination of faults and joint features cause leakage problems at the operational dams in Jordan. Although, preventive measures such as grouting have been implemented, further leakage and/or seepage problems are anticipated and a monitoring system is needed to control and foresee such problems.
Jordan is an earthquake-prone region. Consequently, it is recommended that the design of embankment dams in the vicinity of the Dead Sea-Jordan Valley Rift should include such considerations as dynamic loading and associated hazards, including embankment acceleration zoning, foundation liquefaction risk and rockhead rupture. The magnitude of the design earthquake at each dam site can be estimated following the guidelines of ICOLD (1989), which are based on probabilistic seismic hazard analysis. 相似文献
The hydrogeological study of some karst systems in Lebanon shows important storage capacity, up to 27 billions m3 for Zarka system, the spring of Orontes River. Their geological and morphological settings, as well as their hydrodynamic
function, show structures developed below the level of present springs, probably up to several hundreds meters at depth. Since
Miocene, those carbonate formations were subject to a remarkable instability of their base levels. Variations of sea level,
of which the Messinian salinity crisis is the major phase, and effects of the alpine orogenesis, combined with climate variations
to develop complex, multiphased karst systems. Karstification occurs frequently in the whole formation, often deeply below
sea level or underneath sediment filling of continental basins. The surface karst landscape is often intensely eroded. Those
multiple, superimposed karst phases give the carbonate aquifers their large extension and storage capacity. These karst aquifers
show the typical easy restoration of storage. They have the ability to bear large interannual recharge variations and support
exploitation under high pumping rates. However, these aquifers have some disadvantages for sustainable management. In some
regions, successful boreholes, which allow high pumping rates also induce uncontrolled exploitation. Another consequence is
natural seawater intrusion, as well as the submarine discharge of fresh groundwater, in coastal aquifers. Those carbonate
aquifers are subject to important economical stress which jeopardizes their durability. The systematic study and understanding
of carbonate aquifers in Eastern Mediterranean is a preliminary condition to any integrated and sustainable management of
water resources. Studies in progress in Lebanon may serve as examples to the whole region. 相似文献
A depositional model of the lower Pliocene Hagul formation, which is exposed in the East Cairo district (Egypt), is proposed with more than 10 depositional cycles recognized. Field occurrence, detailed petrographic investigation and geochemical analysis revealed that the sediments within each cycle are the result of three sequential sedimentological processes: (1) alluvial sedimentation, (2) calcretization, and (3) precipitation of palustrine carbonate. It was concluded that Hagul formation has been deposited within the distal part of an alluvial plain during three successive climatic conditions: a humid climate during which alluvial sediments were deposited, a semi-arid climate with episodic precipitation which was favorable for pedogenic calcrete development, and a sub-humid climate during which groundwater level was gradually elevated and groundwater calcrete accumulated. Rising groundwater level continued until shallow wetlands covered the area and palustrine limestone was precipitated. Variations in the thickness and the nature of the host sediment, calcrete and palustrine limestone cycle suggest that each of the sedimentation processes varied from cycle to cycle. 相似文献
Application of the copulas can be useful for the accurate multivariate frequency analysis of hydrological phenomena. There are many copula functions and some methods were proposed for estimating the copula parameters. Since the copula functions are mathematically complicated, estimating of the copula parameter is an effortful work. In the present study, an optimization-based method (OBM) is proposed to obtain the parameters of copulas. The usefulness of the proposed method is illustrated on drought events. For this purpose, three commonly used copulas of Archimedean family, namely, Clayton, Frank, and Gumbel copulas are used to construct the joint probability distribution of drought characteristics of 60 gauging sites located in East-Azarbaijan province, Iran. The performance of OBM was compared with two conventional methods, namely, method of moments and inference function for margins. The results illustrate the supremacy of the OBM to estimate the copula parameters compared to the other considered methods. 相似文献
The aim of this paper was to determine the ultimate vertical bearing capacity of rectangular rigid footings resting on homogeneous peat stabilized by a group of cement deep mixing (CDM) columns. For this purpose, a series of physical modeling tests involving end-bearing and floating CDM columns were performed. Three length/depth ratios of 0.25, 0.5, and 0.75 and three area improvement ratios of 13.1, 19.6, and 26.2 % were considered. Bearing capacity of the footings was studied using different analytical procedures. The results indicated that compared to unimproved peat, the average ultimate bearing capacity (UBC) improvement of floating and end-bearing CDM columns were 60 and 223 %, respectively. The current study found that simple Brom’s method predicted the UBC of the peat stabilized with floating CDM columns with reasonable accuracy, but underestimated the UBC by up to 25 % in the case of end-bearing CDM columns. Published laboratory experiences of stabilizing soft soils using soil–cement columns were also collated in this paper. 相似文献
Groundwater management requires complete visualization of aquifer characteristics to understand scientific aspects and hence remains a challenge, especially in hard rock terrains. In the present research paper, a comprehensive approach using 3D stratigraphic model, fence diagrams and numerical modeling has been proposed to understand the groundwater status for effective recharge. The stratigraphy, groundwater flow, and groundwater fluctuations for the period 1999–2010 were analyzed. The total volume of formations, volume of voids, storage capacity, and quantities of recharge of unconfined aquifer system in the Nagpur urban area were estimated. The steady state groundwater flow model of Basalt formation was calibrated to evaluate the subsurface system using Processing Modflow (PMWIN 5.3.2). The calibrated hydraulic head is compared with field observed head. The comparative spatial analysis presents a simple integrated approach in identifying zones with falling groundwater trends suitable for groundwater recharge in hard rock terrain in Nagpur urban area. 相似文献