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991.
Michel Diament Jean-Claude Sibuet Ahmed Hadaoui 《Geophysical Journal International》1986,86(3):893-907
Summary. Spectral analysis of eight marine gravity profiles and seven SEASAT profiles, combined with corresponding bathymetric data over the Northern Bay of Biscay origin, yield identical admittance functions for wavelengths greater than 120 km. the resulting admittance function has been interpreted in terms of an Airy model of compensation for wavelengths greater than 250 km and in terms of an elastic plate model of compensation for shorter wavelengths. the Airy model corresponds to a crustal thickness variation across the margin. the plate model with an elastic thickness of 8 km is associated with the regional compensation of a sedimentary load which was probably emplaced during and just after rifting. 相似文献
992.
The Pan-African basement exposed in the Meatiq area west of Quseir, Egypt, consists of an infracrustal basement overthrusted by a supracrustal cover. The infracrustal rocks were developed as a result of an old orogeny referred to as the Meatiqian orogeny where granite—gneiss, migmatitic gneisses and migmatized amphibolites were formed. The granite—gneiss represents a deformed granite pluton emplaced at 626±2 Ma, whereas the migmatitic gneisses and amphibolites are of mixed igneous and sedimentary parentage. In view of the data so far available, the nature of the Meatiqian orogeny could not be deciphered. In spite of the young isotopic ages, it is suggested that at least the metasedimentary gneisses represent older rocks in the stratigraphic sequence of the infracrustal basement.The supracrustal cover represents a part of an extensive ophiolitic mélange obducted onto the infracrustal basement during the next orogeny (Abu Ziran orogeny) which culminated at 613±2 Ma. An active continental margin-type regime can adequately explain the evolution of such a supracrustal cover. During obduction, the ophiolitic mélange and the upper 2 km thick part of the infracrustal basement were intensely deformed and metamorphosed under PT conditions of the greenschist—epidote amphibolite facies. The deformed infracrustal basement was converted into mylonitic—blastomylonitic rocks and schists composing five thrust sheets, and subsequently intruded by synkinematic granitoid sheets. Later, both the infracrustal basement and the overlying supracrustal cover were isostatically uplifted, subjected to complex shallow folding giving rise to the major Meatiq domal structure, and were intruded by a postkinematic adamellite pluton at 579±6 Ma. 相似文献
993.
Ahmed Aly Kamel 《Celestial Mechanics and Dynamical Astronomy》1969,1(2):190-199
The theory of perturbation based on Lie transforms is considered. Deprit's equation is reduced to a form which enables us to generate simplified general recursion formulae. These expansions are then modified to speed up the implementation of such perturbation theory in the computerized symbolic manipulation. 相似文献
994.
995.
Ahmed E. Radwan 《Astrophysics and Space Science》1989,159(2):279-293
The method of Fourier analysis of the light changes in the frequency-domain has been studied and discussed for 92 light curves of different types of eclipsing binary systems.Geometrical and physical elements of the systems under analysis have been listed and discussed, accordingly the advantages and disadvantages of the method is presented.The results show that the method is suitable for analysis of detached and most of the semi-detached systems, while for contact binaries and -Lyrae-type stars it has some difficulties. The light curve synthesis method is recommended. 相似文献
996.
Egypt is recognized as a moderate seismicity region where earthquakes are distributed within several active regions. Owing
to sparse distribution of both seismicity and seismic stations, mostly moderate-size Egyptian earthquakes were recorded by
regional stations. One of such cases is the moderate-size earthquakes of moment magnitudes greater than 4.0 which struck the
Western Desert of Egypt in 1998 and 1999. These events are the first instrumentally recorded earthquakes occurring in the
area. In the present study, the source mechanism for these earthquakes was estimated using the waveform data recorded from
one of the very broadband MedNet seismograph stations and polarities from the national short-period seismographs. An iterative
technique was applied to find the best-fit double-couple mechanism by a grid search over strike, dip and rake. Regional synthetic
seismograms were calculated by using f–k integration in the frequency range of 0.03–0.1 Hz. A crustal structure fitted to surface wave dispersion curves was used
to compute Green’s function. Focal depths were determined through the grid search method for a range of source depths. Our
results show a normal faulting mechanism with minor strike-slip component. The NNW trend has been chosen as a preferred rupture
plane in consistence with surface and subsurface faults and microearthquake seismicity in the epicenteral area as well. 相似文献
997.
Nasr Yousef M. J. Omar M. Radzi Bin Abas Noorsaadah A. Rahman Norhayati Mohd. Tahir Ahmed I. Rushdi Bernd R. T. Simoneit 《Environmental Geology》2007,52(8):1485-1500
The concentrations of n-alkanes, unresolved complex mixture (UCM), petroleum molecular markers, other tracers of cooking and burning emissions, and
natural background in atmospheric particles and roadside dust particles were measured at eight locations in the city center
and the suburbs of Kuala Lumpur, Malaysia. Atmospheric particles were collected using high-volume filtration (PM-10, GFF)
over 24 h average periods. Road dusts were swept up, dried and sieved. Both types of samples were extracted with dichloromethane/methanol
mixture (3:1 v/v) by ultrasonic agitation. The extracts were then fractionated by column chromatography and the alkanes subjected
to gas chromatography–mass spectrometry (GC–MS). Total extracts were also analyzed directly by GC–MS after silylation. The
molecular distributions of compounds as well as diagnostic geochemical ratios were determined in order to identify the sources
of the organic compounds. Samples collected from a rural area and lubricating oils were also analyzed for comparisons. Anthropogenic
and biogenic sources such as vehicular emissions, waxes of higher plants, food cooking operations, and biomass and domestic
refuse burning processes contributed to the organic matter content of atmospheric and to lesser extent, roadside dust particles. 相似文献
998.
Compressibility of porous rocks: Part II. New relationships 总被引:1,自引:0,他引:1
Ali Ahmed Jalalh 《Acta Geophysica》2006,54(4):399-412
Pore volume compressibility is one of the physical properties of a reservoir that must be specified in many reservoir-engineering
calculations. The main objective of this work is to provide new general formulas for pore volume compressibility versus porosity
on the basis of measured compressibilities of some limestone and sandstone rocks in a wide range of porosity values and of
varied type; the measurements were performed on Hungarian reservoir rock samples. The obtained laboratory results were compared
with the published correlations of consolidated limestone samples as well with values for friable and strongly consolidated
sandstones. The validity of using compressibility data from the literature was investigated. The measured data showed poor
agreement with the published correlations.
The first approach to find better and more accurate rock compressibility correlations consisted of combing all the data available
from the literature, using the same formula of Horne’s type. However, this attempt did not give satisfying fitting results.
In the next step, by using twelve different fitting formulas, and other comprehensive nonlinear fitting regression programs,
new rock compressibility correlations for limestone and sandstone rocks, with better goodness of fit, were developed. These
new correlations can be generalized and used for most of oil and gas reservoirs. 相似文献
999.
Ireneusz Malik 《地球表面变化过程与地形》2006,31(10):1227-1245
The Ma?a Panew is a meandering river that flows 20 km through a closed forest. During times of high discharge the riverbed and floodplain are transformed under the influence of riparian trees. The changes provide the opportunity to measure the intensity of erosion and sediment accumulation based on tree ages, the dating of coarse woody debris (CWD) in the riverbed, and the dating of eccentric growth of tilting trees and exposed roots. The bed and floodplain in reaches of the Ma?a Panew River with low banks were greatly altered as a result of long periods of flooding between 1960 and 1975. Banks were undercut during these floods and black alders tilted. Those parts of alder crowns or stems which tilt and sink generate small sand shadows. When erosion is intensive alder clumps are undercut from concave banks and become mid‐channel islands, while on the other side of the channel meandering bar levels are created. The reaches with higher banks were altered by large floods, especially in 1985 and 1997. The concave banks are undercut and sediment with CWD is deposited within the riverbed, forming sand shadows behind the CWD. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
1000.
Methods for diagnostics of the state of hydraulic structures are considered. The control equipment is shown to be applicable to earthquake prediction, and the role that monitoring of hydraulic structures constructed in the permafrost zone can play in the improvement of normative documents and the development of the theory and practice of hydraulic construction in northern regions is assessed. The experience in studying the environmental effect of Sayano–Shushenskaya Hydropower Plant (HPP) is characterized. The major tasks of the improvement of monitoring system are formulated. 相似文献