U-Pb (zircon) ages for the gneissic terrane west of the Nile,southern Egypt     

M. Sultan  R. D. Tucker  Z. El Alfy  R. Attia  Abdel Ghany Ragab 《International Journal of Earth Sciences》1994,83(3):514-522

The first U-Pb zircon ages are reported for the gneissic bedrock inliers previously interpreted as part of the Nile Craton. The inliers crop out in the Egyptian Western Desert, east of the Uweinat area and west of the Eastern Desert. Multi- and single-grain zircon analyses of granitoid gneiss and migmatite from Gebel Um Shagir, Aswan, and another locality approximately 160 km south-west of Aswan, yield simple discordia with near modern day Pb loss trajectories, and the following Neoproterozoic crystallization ages: 626+4/–3, 634 ± 4 and 741 ± 3 Ma. In contrast, multi- and single-grain U-Pb analyses (zircon and sphene) from an anorthositic gabbro at Gebel Kamil (22°46N 26°21E) and an anorthosite at Gebel El Asr (22°46N 31°10E) yield Archean and Paleoproterozoic emplacement ages. The former yield a crystallization age of > 2.67 Ga and a metamorphic age of 2.0 Ga; the latter a metamorphic age of 0.69 Ga and an inheritance age of 1.9–2.1 Ga. Because high grade gneiss and migmatite of Neoproterozoic, Paleoproterozoic and Archean age crop out west of the Nile, pre-Neoproterozoic crust should no longer be identified by its metamorphic grade. By contrast, mapping the anorthosite and related rocks might provide first-order estimates for the extension of pre-Neoproterozoic crust in north-east Africa. It is suggested that Archean and Paleoproterozoic crust of the Uweinat and Congo Craton are contiguous because these U-Pb (zircon) data show no evidence for a Neoproterozoic thermal overprint in the Gebel Kamil area and there is no pronounced Neoproterozoic magmatic activity south of the Uweinat inlier and north of the Congo Craton.  相似文献   

Radiation transfer for linearly anisotropic phase functions     

M. S. Abdel Krim 《Astrophysics and Space Science》1990,164(1):69-77

Radiative transfer equation in a plane-parallel medium with isotropic boundary conditions for linearly anisotropic scattering phase function is considered. Two coupled integral equations for total density of radiation and total radiation flux are obtained. The Galerkin method is used to solve these equations. Numerical results for the radiative fluxes at the boundaries show that the Galerkin method yields accurate results compared well with other exact methods.  相似文献   

Preliminary evidence of a link between surface soil properties and the arsenic content of shallow groundwater in Bangladesh     

A. van Geen  Z. Aziz  A. Horneman  B. Weinman  R.K. Dhar  Y. Zheng  S. Goodbred  R. Versteeg  A.A. Seddique  M.A. Hoque  K.M. Ahmed 《Journal of Geochemical Exploration》2006,88(1-3):157

The extremely heterogeneous distribution of As in Bangladesh groundwater has hampered efforts to identify with certainty the mechanisms that lead to extensive mobilization of this metalloid in reducing aquifers. We show here on the basis of a high-resolution transect of soil and aquifer properties collected in Araihazar, Bangladesh, that revealing tractable associations between As concentrations in shallow (< 20 m) groundwater with other geological, hydrological, and geochemical features requires a lateral sampling resolution of 10–100 m. Variations in the electromagnetic conductivity of surface soils (5–40 mS/m) within a 500 m × 200 m area are documented with 560 EM31 measurements. The results are compared with a detailed section of groundwater As concentrations (5–150 μg/L) and other aquifer properties obtained with a simple sampling device, “the needle-sampler”, that builds on the local drilling technology. By invoking complementary observations obtained in the same area and in other regions of Bangladesh, we postulate that local groundwater recharge throughout permeable sandy soils plays a major role in regulating the As content of shallow aquifers by diluting the flux of As released from reducing sediments.  相似文献   

A New Spectral Index for Extraction of Built-Up Area Using Landsat-8 Data     

Sara Bouzekri  Abdel Aziz Lasbet  Ammar Lachehab 《Journal of the Indian Society of Remote Sensing》2015,43(4):867-873

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A climatological analysis of Saharan cyclones   总被引：1，自引：0，他引：1  

K. Ammar  Mossad El-Metwally  Mansour Almazroui  M. M. Abdel Wahab 《Climate Dynamics》2014,43(1-2):483-501

In this study, the climatology of Saharan cyclones is presented in order to understand the Saharan climate, its variability and its changes. This climatology includes an analysis of seasonal and interannual variations, the identification and classification of cyclone tracks, and a presentation of their chief characteristics. The data used are drawn from the 1980–2009, 2.5° × 2.5°, NCEP/NCAR reanalysis (NNRP I) dataset. It is found that cyclone numbers increase in September–October–November (SON) at 4.9 cyclones per decade, while they decrease in June–July–August at 12.3 cyclones per decade. The identification algorithm constructed 562 tracks, which are categorized into 12 distinct clusters. Around 75 % of the Saharan cyclones originate south of the Atlas Mountains. The percentage of tracks that move over the Sahara is around 48 %. The eastern Mediterranean receives 27 % of the Saharan tracks, while the western basin receives only 17 and 8 % of all the Saharan cyclones decay over the Arabian Peninsula. The maximum cyclonic activity occurs in April. There is a general decrease in the number of tracks in all categories between 1993 and 2009, compared with the period between 1980 and 1992. About 72 % of the Saharan cyclones do not live more than 3 days, and about 80 % of the cyclones in the tracks never reach central pressures 1,000 hPa during their lifetimes. The maximum deepening in the tracks occurs over the western Mediterranean and over northern Algeria.  相似文献   

Integrated remote sensing data utilization for investigating structural and tectonic history of the Ghadames Basin,Libya     

N.M. Saadi  M. Abdel Zaher  F. El-Baz  K. Watanabe 《International Journal of Applied Earth Observation and Geoinformation》2011

This study was initiated to constrain the geological structure of the Ghadames Basin in northwest Libya. Detailed analysis was based on digital integration of surface data, including SRTM DEM, ETM+ and geologic maps with subsurface data, including well logs and potential field data. Integrated analysis of remotely sensed data of the SRTM and ETM+ were utilized to identify geologic lineaments in the area. Ground-based verification of the remote sensing data was achieved with field work. Interpretation and analysis of the lineaments indicate that the Ghadames Basin is controlled by four main fault systems that trend WNW, NNW, NW and ENE. Well logs and potential field data were used to delineate a detailed picture of the subsurface structure. The potential field data reveal two NE and NNE trending sedimentary basins. The depth of the basement inside the main basin ranges from 2 to 6 km. A two-dimensional (2-D) schematic model shows that the basin gradually deepens towards the southwest. The applied data integration gave new insight into the tectonic and structure patterns of the Ghadames Basin and the adjacent areas of northwest Libya.  相似文献   

Harmonic by harmonic removal technique for improving vibroseis data quality     

Abd El‐Aziz Khairy Abd El‐Aal 《Geophysical Prospecting》2011,59(2):279-294

In this paper, an improved method is presented to reduce vibrator harmonic distortion, one harmonic at a time and the method is illustrated with both simulated and field data. This method improves on the previous method that treated all the harmonics at once. The significant contribution in this procedure is a considerable reduction for the harmonics without any alteration for the weakest signals possibly present in positive and negative times. The core of the proposed technique depends on an accurate simulation for all the harmonics one by one existing in the positive and negative times of the data after cross‐correlation with the fundamental sweep and then subtracting the simulated harmonics from the original data using an optimization procedure. The steps and mathematical equations of the procedure are explained in detail in the body of the article in the section titled ‘harmonic by harmonic attenuation procedure’. Accordingly, a well‐developed procedure for enhancing the vibroseis data quality in both down‐ and up‐sweep data is illustrated. The procedure was tested on both synthetic and field data sets.  相似文献   

Ground motion spatial variability effects on seismic response control of cable-stayed bridges     

Shehata E. Abdel Raheem  Toshiro Hayashikawa  Uwe Dorka 《地震工程与工程振动(英文版)》2011,10(1):37-49

The spatial variability of input ground motion at supporting foundations plays a key role in the structural response of cable-stayed bridges (CSBs); therefore, spatial variation effects should be included in the analysis and design of effective vibration control systems. The control of CSBs represents a challenging and unique problem, with many complexities in modeling, control design and implementation, since the control system should be designed not only to mitigate the dynamic component of the structural response but also to counteract the effects of the pseudo-static component of the response. The spatial variability effects on the feasibility and efficiency of seismic control systems for the vibration control of CSBs are investigated in this paper. The assumption of uniform earthquake motion along the entire bridge may result in quantitative and qualitative differences in seismic response as compared with those produced by uniform motion at all supports. A systematic comparison of passive and active system performance in reducing the structural responses is performed, focusing on the effect of the spatially varying earthquake ground motion on the seismic response of a benchmark CSB model with different control strategies, and demonstrates the importance of accounting for the spatial variability of excitations.  相似文献   

Recharge and contamination sources of shallow and deep groundwater of pleistocene aquifer in El-Sadat industrial city: isotope and hydrochemical approaches     

M. A. Ahmed  S. G. Abdel Samie  H. M. El-Maghrabi 《Environmental Earth Sciences》2011,62(4):751-768

Hydrochemical and isotopic researches were conducted in El-Sadat City groundwater system to identify groundwater alteration, recharge, residence time and extent of pollution. The groundwater salinity gradually increases as the groundwater moves from northeastern to southwestern parts of the city. Groundwater generally shows mineralization decreasing with depth, indicating that the possibility of recent water penetration far below the surface is limited. Shallow groundwater has an elevated level of nitrate, which is attributed to anthropogenic sources due to intensive agricultural activity. The limit of high nitrate water may mark the maximum penetration of groundwater from the surface, which is found in depths <100 m. The northeastern and southwestern industrial areas are highly contaminated by some heavy metals, which may originate from some local industrial effluents. The sewage oxidation ponds seem to show no effect on groundwater; hence, these ponds are not a point source for these heavy metals. Dissolved ions depict five different hydrochemical facies, and stable isotopes define the recharge mechanisms, the origin of groundwater and the hydraulic confinement of deep groundwater. The deep groundwater is untritiated and has long residence times (in the order of thousands of years). Three different hydrochemical groups have been recognized and mapped in El-Sadat City, based on the chemical and isotopic information of the groundwater. These groups have different levels of contamination. The deep groundwater samples are significantly less impacted by surface activities and it appears that these important water resources have very low recharge rates and would, therefore, be severely impacted by overabstraction. The extensive exploitation of groundwater for drinking water supply would shortly be reflected by a gradual decline of the groundwater table in El-Sadat City. Amelioration of groundwater quality requires further management strategies and efforts in the forthcoming years.  相似文献   

Strong ground motion attenuation in Aswan area, Egypt     

A. Deif  Azza Abed  Kamal Abdel-Rahman  Enayat Abdel Moneim 《Arabian Journal of Geosciences》2011,4(5-6):855-861

Recent and paleo seismicity indicate that moderate seismic activity is relatively large for Aswan area. This is a warning on the possibility of occurrence of earthquakes in the future too. No strong motion records are available in Aswan area for engineers to rely upon. Consequently, the seismological modeling is an alternative approach till sufficient instrumental records around Aswan become available. In the present study, we have developed new ground motion attenuation relationship for events spanning 4.0?≤? M _w?≤?7.0 and distance to the surface projection of the fault up to 100 km for Aswan based on a statistically simulated seismological model. We generated suites of ground motion time histories using stochastic technique. The ground motion attenuation relation describes the dependence of the strength of the ground motions on the earthquake magnitude and distance from the earthquake. The proposed equation for peak ground acceleration (PGA) for the bed rock is in the form of: $ {\mathbf{log}}{\text{ }}\left( {{\mathbf{PGA}}/{\mathbf{gal}}} \right){\text{ }} = {\mathbf{1}}.{\mathbf{24}} + {\mathbf{0}}.{\mathbf{358}}{M_{\mathbf{w}}} - {\text{ }}{\mathbf{log}}\left( {\mathbf{R}} \right){\text{ }}-{\text{ }}{\mathbf{0}}.{\mathbf{008}}{\text{ }}{\mathbf{R}}{\text{ }} + {\text{ }}{\mathbf{0}}.{\mathbf{22}}{\text{ }}{\mathbf{P}} $ . Where PGA is the peak ground acceleration in gal (cm/s²); M_w, its moment magnitude; R is the closest distance between the rupture projection and the site of interest; and the factor P is a dummy variable. It is observed that attenuation of strong motion in Aswan is correlated with those used before in Egypt.  相似文献