排序方式： 共有49条查询结果，搜索用时 31 毫秒
21.
J. Besse F. Torcq Y. Gallet L. E. Ricou L. Krystyn & A. Saidi 《Geophysical Journal International》1998,135(1):77-92
A palaeomagnetic study of Late Permian to early Jurassic rocks from the Alborz and Sanandaj–Sirjan zones in Iran and a compilation of selected palaeopoles from the Carboniferous to the present provide an updated history of the motion of the Iranian block within the Tethys Ocean. The Iran assemblage, part of Gondwana during the Palaeozoic, rifted away by the end of the Permian. We ascertain the southern-hemisphere palaeoposition of Iran at that time using magnetostratigraphy and show that it was situated close to Arabia, near to its relative position today. A northward transit of this block during the Triassic is shown, with an estimated expansion rate of the Neotethyan ridge of 100–140 km Myr−1 . The northward convergence with respect to Eurasia ended during the Ladinian (Middle Triassic), and is marked by a collision in the northern hemisphere with the Turan platform, which was the southern margin of the Eurasian continent at that time. No north–south component of shortening is evidenced north of Iran afterwards. An analysis of the declinations from the Late Permian to the present shows different, large rotations, emphasizing the important tectonic phases suffered since the Triassic. Finally, we propose palaeomagnetic reconstructions of the Tethys area during the Late Permian and the Late Triassic, showing that the Palaeotethys Ocean was narrower than previously thought, and did not widen its gate to the Panthalassa before the Triassic period. 相似文献
22.
Salwa Saidi 《水文科学杂志》2013,58(2):288-304
Abstract The assessment of groundwater vulnerability to pollution has proved to be an effective tool for water resource management, especially in arid and semi-arid regions like Mahdia and Ksour Essaf. The main objective of this study is to assess the aquifer vulnerability by applying the DRASTIC method as well as using sensitivity analysis to evaluate the effect of each DRASTIC parameter on the final vulnerability map. An additional objective is to demonstrate the role of the GIS techniques in the vulnerability assessment. The DRASTIC method assigns a high vulnerability to the coast of the Mahdia-Ksour Essaf. The lowest values are observed in the southern part of the study area. A sensitivity analysis applied in this study suggests that net recharge, aquifer media and depth of groundwater are the key factors determining vulnerability. The model is validated with groundwater quality data and the results have shown strong relationships between modified DRASTIC Vulnerability Index and nitrate and chloride concentrations. Citation Saidi, S., Bouri, S. & Ben Dhia, H. (2011) Sensitivity analysis in groundwater vulnerability assessment based on GIS in the Mahdia-Ksour Essaf aquifer, Tunisia: a validation study. Hydrol. Sci. J. 56(2), 288–304. 相似文献
23.
Ikram Jmal Bachaer Ayed Emna Boughariou Nabila Allouche Salwa Saidi Monji Hamdi Salem Bouri 《Arabian Journal of Geosciences》2017,10(16):364
The study region comprises the Sidi Bouzid shallow aquifer, which is located in the western part of Central Tunisia. It is mainly occupied by agricultural land with intensive use of chemical fertilizers especially nitrates. For this reason, nitrate measurement was performed in 38 water samples to evaluate and calibrate the obtained models. Several environmental parameters were analyzed using groundwater nitrate concentrations, and different statistical approaches were applied to assess and validate the groundwater vulnerability to nitrate pollution in the Sidi Bouzid shallow aquifer. Multiple linear regression (MLR), analyses of covariance (ANCOVA), and logistic regression (LR) were carried out for studying the nitrate effects on groundwater pollution. Statistical analyses were used to identify major environmental factors that control the groundwater nitrate concentration in this region. Correlation and statistical analyses were conducted to examine the relationship between the nitrate (dependent variable) and various environmental variables (independent variables). All methods show that “groundwater depth” and “land use” parameters are statistically significant at 95% level of confidence. Groundwater vulnerability map was obtained by overlaying these two thematic layers which were obtained in the GIS environment. It shows that the high vulnerability area coincides with the likelihood that nitrate concentration exceeds 24.5 mg/l in groundwater. The relationship between the groundwater vulnerability classes and the nitrate concentrations provides satisfactory results; it showed an Eta-squared correlation coefficient of 64%. So, the groundwater vulnerability map can be used as a synthetic document for realistic management of groundwater quality. 相似文献
24.
Groundwater vulnerability and risk mapping of the Hajeb-jelma aquifer (Central Tunisia) using a GIS-based DRASTIC model 总被引：7，自引：2，他引：5
The aim of this study is to elaborate a synthetic document for the assessment of groundwater vulnerability to pollution in the Hajeb-Jelma aquifer. The specific object is to incorporate the Geographical Information System (GIS) to generate groundwater vulnerability and risk maps with DRASTIC model. Indeed, GIS could help to make the results of a complicated model more clear through visual representation, providing an applicable tool for decision makers. The vulnerability map of Hajeb-Jelma watershed shows three classes: moderate, high and very high depending on the intrinsic properties. The risk map shows a very high risk dependant on hydrogeological characteristics, land use and human impacts in major part of the Hajeb-Jelma region. These maps could serve as a scientific basis for sustainable land use planning and groundwater management in the Hajeb-Jelma region. 相似文献
25.
In this research, we have focused on the geometrical characteristics of young faults in North Tehran tectonic wedge which is confined with the Mosha and North Tehran faults, the most outstanding active faults in Alborz fold-thrust belt. The statistical, genetic, and kinematic relationships between internal faults, boundary faults, and the stress regime in the area (at the finite state of deformation path) are considered in detail with the help of rose diagrams and Riedel??s model. On this basis, all faults with diverse mechanisms have been classified into different Riedel fractures and their orders of formation are identified. Pattern of faults implies a more or less N?CS compression at the period of faulting. Consideration of geometry and tectonic setting of abundant normal faults have led to propose folding and listric faulting model to explain the origin of normal faults in a compressional tectonic region. These structural models represent the mechanism of normal faulting in response to compression in crustal and upper crustal scales, respectively. 相似文献
26.
利用NCEP 1°×1°格点再分析、FY-2E相当黑体亮温TBB和地面加密自动气象站等资料,分析了辽宁3次典型长历时强降水TBB值与降水强度的关系、中尺度环境场特征及维持机制,并初步建立了辽宁长历时强降水概念预报模型。结果表明:在副热带高压的形态、位置和强度有利于辽宁产生强降水的大尺度形势下,副热带高压西侧低空急流持续输送的充沛暖湿空气与高空干冷空气在同一地点长时间相互作用,为强降水的发生和维持提供了有利的环境背景条件。强降水持续时间与其上空的强垂直速度持续时间有很好的对应关系,强降水持续时高空一般为弱的不稳定或中性层结。强降水不仅可出现在对流云团发展旺盛的冷云区内部或边缘,也可发生在TBB值较小的暖云区内。TBB值的大小与降水强度没有必然的关系,但TBB值的快速减小都预示强降水即将发生。这些结论有利于深化认识辽宁地区长历时强降水的成因并为预报提供线索。 相似文献
27.
Abderrahmane Soulaimani Mohammed Jaffal Lhou Maacha Azzouz Kchikach Abdessamad Najine Abdellatif Saidi 《Comptes Rendus Geoscience》2006,338(3):153-160
Aeromagnetic data of the Anti-Atlas Mountains show an important magnetic anomaly along the ‘Major Anti-Atlas Fault’, produced by different mafic and ultramafic rocks of a Neoproterozoic ophiolite complex. The magnetic modelling of Bou Azzer–El Graara ophiolitic suture shows a deep-seated anomaly through the upper continental crust corresponding to a north-dipping subduction. The polarity of the Pan-African subduction in the Anti-Atlas is therefore compatible with the contemporaneous Pan-African orogenic belts, where polarity of subduction dipped away from the West African Craton during the amalgamation of Western Gondwana. To cite this article: A. Soulaimani et al., C. R. Geoscience 338 (2006). 相似文献
28.
In order to isolate the effect of grain size and cementation on the mechanical behaviour of poorly consolidated granular rock, we prepared synthetic rock samples in which these two parameters were varied independently. Various proportions of sand, Portland cement and water were mixed and cast in a mold. The mixture was left pressure-free during curing, thus ensuring that the final material was poorly consolidated. We used two natural well-sorted sands with grain sizes of 0.22 and 0.8 mm. The samples were mechanically tested in a uniaxial press. Static Young's modulus was measured during the tests by performing small stress excursions at discrete intervals along the stress–strain curves. All the samples exhibited nonlinear elasticity, i.e., Young's modulus increased with stress. As expected, we found that the uniaxial compressive strength increased with increasing cement content. Furthermore, we observed a transition from grain size sensitivity of strength at cement content less than 20–30% to grain size independence above this value. The measured values of Young's modulus are well explained by models based on rigid inclusions embedded in a soft matrix, at high cement content, and on cemented grain-to-grain contacts, at low cement content. Both models predict grain size independence in well-sorted cemented sands. The observed grain size sensitivity at low cement content is probably due to microstructural differences between fine- and coarse-grained materials caused by small differences in grain sorting quality. 相似文献
29.
A Hafid J.P Sagon M Julivert M.L Arboleya A Saquaque A El-Boukhari A Saidi J.M.F Soler 《Journal of African Earth Sciences》2001,32(4):2195
Before the Pan-African Orogeny, the Palæoproterozoic basement and its Neoproterozoic cover (limestones and quartzites) of the Zenaga Inlier were cross-cut by a swarm of doleritic dykes. They are more or less altered. The primary mineral assemblage consists of plagioclase, clinopyroxene, very rare orthopyroxene, ilmenite, apatite, micropegmatite and sometimes hornblende and biotite. Mineralogical and geochemical studies indicate that the dolerites are continental tholeiites. Two groups of dykes have been distinguished. Accordingly, rare earth elements, P2O5, Zr, Th, Ba and Sr contents are higher in group I than in group II, which is richer in V. Group I comprises the north-south and northwest-southeast swarms, while group II corresponds to northeast-southwest and east-west swarms, which were emplaced later. These geochemical variations may be explained by a higher degree of melting of the mantle source for the later group II. Doleritic dykes of Zenaga had been emplaced during an extensional episode, prior to Pan-African folding. 相似文献
30.
Helmi Saidi Marzia Ciampittiello Claudia Dresti Laura Turconi 《Environmental Earth Sciences》2014,72(11):4607-4616
With regard to extreme events, it is well documented that an intensity of about 1 mm/min already represents an extreme intensity. Under alpine conditions, a precipitation event with an intensity of 3 mm/min has occurred. Therefore, the rain gauges in this region have to be able to measure in this and even in higher intensity ranges. This study deals with basic automated tipping-bucket rain (TBR) gauge and Bulk precipitation samplers, which are able to hold more than 95 % of the cumulative rainfall, that are verified within the space of the week without losses during the extreme events and with minimal evaporation loss. Bulk samplers collected more rainfall than TBR gauges in 110 of 221 extreme events analysed over the past 10 years. In 17 extreme events, an underestimation greater than 10 % was evaluated. The objective was to single out the counting errors associated with TBR gauge, during extreme events, so as to help the understanding of the measured differences between instruments in the field. We want to determine whether the automated precipitation gauge can provide a reliable and precise measurement of precipitation with particular interest regarding heavy and extreme events. 相似文献