A Stress Release Model in Egypt     

Omar  Kh. A.  Mangira  O. 《Geotectonics》2020,54(1):106-112

Geotectonics - The complexity of seismogenesis calls for probabilistic rather than deterministic model. Towards that direction, the stress release models transpose the elastic rebound theory in a...  相似文献   

Development of an infinite element boundary to model gravity for subsurface civil engineering applications     

Twana Kamal Haji  Asaad Faramarzi  Nicole Metje  David Chapman  Farough Rahimzadeh 《国际地质力学数值与分析法杂志》2020,44(3):418-431

The accurate modelling of gravity is of crucial importance for a variety of issues including, but not restricted to, the identification of buried objects. Gravity is an unbounded problem, which causes challenges when applying numerical models, i..e.., it results in computational difficulties when specifying the relevant boundary conditions. In order to address this, previous research has tended to generate artificial boundary conditions, e.g., truncating the simulated domain and adding many unrealistic zero-density layers, which introduces more unknown parameters and unnecessarily excessive computational time. In order to overcome such inaccuracies, this paper proposes an innovative development of the finite element modelling technique, which represents a step change in the field of gravity forward modelling. A comprehensive formulation of an infinite element to reproduce the far-field boundary effect using only one layer of infinite elements is presented. The developed model considerably reduces the computational time while obtaining high degrees of accuracy. The model is validated against the exact solution of the problem, and its results show an excellent performance. The proposed method can significantly improve the postprocessing and interpretation stages of data analysis relevant to micro-gravity sensors. The new method is applied to subsurface civil engineering although its applicability is manifold.  相似文献   

Termination of intra‐arc rifting at ca 16 Ma in the Southwest Japan arc: The tectonostratigraphy of the Hokutan Group     

Toshiki Haji  Atsushi Yamaji 《Island Arc》2020,29(1)

Miocene intra‐arc rifting associated with the opening of the Japan Sea formed grabens in several areas in Southwest (SW) Japan, but the extensional tectonics of the arc are still not well understood. In this study, we first document the tectonostratigraphy of the Hokutan Group in the northwestern part of the Kinki district, and demonstrate the termination of extensional tectonics at ca 16.5 Ma, as inferred from grabens in the lower part of the group being unconformably overlain by sediments of the upper part. Second, we review early Miocene grabens in SW Japan to suggest that intra‐arc rifting was abandoned at ca 16 Ma, essentially simultaneously with the end of rotation of the SW Japan arc as evidenced by paleomagnetic studies. The lesser numbers of grabens and reduced thicknesses of graben fills suggest that extensional deformation of the SW Japan arc was significantly weaker than that of the Northeast (NE) Japan arc, which was broken into blocks, indicating various degrees of paleomagnetic rotation within NE Japan. The weak deformation has allowed paleomagnetic studies to infer the coherent rotation of the SW Japan arc.  相似文献   

Hydrocarbon Generation,In-Source Conversion of Oil to Gas and Expulsion: Petroleum System Modeling of the Duwi Formation,Gulf of Suez,Egypt     

Ahmed  Mohammed A.  Hegab  Omar A.  Awadalla  Ahmed Sh.  Farag  Ali E.  Hassan  Saad 《Natural Resources Research》2019,28(4):1547-1573

Natural Resources Research - A multiple forward 1D modeling approach on four wells in the Abu Rudeis-Sidri oil field has been performed in accordance with the plate tectonics and crustal...  相似文献   

Threats to sandy beach ecosystems: A review     

Omar Defeo  Anton McLachlan  David S. Schoeman  Thomas A. Schlacher  Jenifer Dugan  Alan Jones  Mariano Lastra  Felicita Scapini 《Estuarine, Coastal and Shelf Science》2009

We provide a brief synopsis of the unique physical and ecological attributes of sandy beach ecosystems and review the main anthropogenic pressures acting on the world's single largest type of open shoreline. Threats to beaches arise from a range of stressors which span a spectrum of impact scales from localised effects (e.g. trampling) to a truly global reach (e.g. sea-level rise). These pressures act at multiple temporal and spatial scales, translating into ecological impacts that are manifested across several dimensions in time and space so that today almost every beach on every coastline is threatened by human activities. Press disturbances (whatever the impact source involved) are becoming increasingly common, operating on time scales of years to decades. However, long-term data sets that describe either the natural dynamics of beach systems or the human impacts on beaches are scarce and fragmentary. A top priority is to implement long-term field experiments and monitoring programmes that quantify the dynamics of key ecological attributes on sandy beaches. Because of the inertia associated with global climate change and human population growth, no realistic management scenario will alleviate these threats in the short term. The immediate priority is to avoid further development of coastal areas likely to be directly impacted by retreating shorelines. There is also scope for improvement in experimental design to better distinguish natural variability from anthropogenic impacts. Sea-level rise and other effects of global warming are expected to intensify other anthropogenic pressures, and could cause unprecedented ecological impacts. The definition of the relevant scales of analysis, which will vary according to the magnitude of the impact and the organisational level under analysis, and the recognition of a physical–biological coupling at different scales, should be included in approaches to quantify impacts. Zoning strategies and marine reserves, which have not been widely implemented in sandy beaches, could be a key tool for biodiversity conservation and should also facilitate spillover effects into adjacent beach habitats. Setback and zoning strategies need to be enforced through legislation, and all relevant stakeholders should be included in the design, implementation and institutionalisation of these initiatives. New perspectives for rational management of sandy beaches require paradigm shifts, by including not only basic ecosystem principles, but also incentives for effective governance and sharing of management roles between government and local stakeholders.  相似文献   

Using hydrochemical,stable isotope,and river water recharge data to identify groundwater flow paths in a deeply buried karst system          下载免费PDF全文

Dajun Qin  Zhanfeng Zhao  Yi Guo  Wencai Liu  Muhammed Haji  Xiaohong Wang  Baodong Xin  Yu Li  Yong Yang 《水文研究》2017,31(24):4297-4314

The deeply buried river‐connected Xishan karst aquifer (XKA) in western Beijing, China, has been suffering from diminishing recharge for several decades, which in turn leads to the disappearing of spring water outflows and continuously lowering of groundwater level in the area. Thus, it is important to correctly recognize the groundwater recharge and flow paths for the sustainable development of the XKA. To investigate these issues, the hydrochemical and isotopic compositions are analysed for both surface water and groundwater samples collected over an area of about 280 km². Results show that (a) the river water is characterized by high Na contents; (b) the δ²H and δ¹⁸O values in the river water are distinctively higher than those of groundwater samples, after experiencing the long‐time evaporative enrichment in the upstream reservoir; (c) the Sr concentrations and ⁸⁷Sr/⁸⁶Sr ratios of groundwater clearly indicated the interaction between water and carbonate minerals but excluded the water–silicate interaction; and (d) the groundwater samples in the direct recharge area of the XKA have the lowest Na concentrations and the δ²H and δ¹⁸O values. Based on the large differences in the Na contents and ¹⁸O values of groundwater and surface water, a simple two‐component mixing model is developed for the study area and the fractions of the river water are estimated for groundwater samples. We find that the distribution pattern of the river water fractions in the XKA clearly shows a change of directions in the preferential flow path of the groundwater from its source zone to the discharge area. Overall, our results suggest that the recharged surface water can be a useful evidence for delineating the groundwater flow path in river‐connected karst aquifer. This study improves our understanding of the heterogeneity in karst groundwater systems.  相似文献   

The Spatial Structure of Zooplankton Communities of Pedu Reservoir, Malaysia     

Johan Ismail  Diana Latief 《湿地科学》2012,10(4):423-428

A total of 22 species of zooplankton were identified from 8 sampling stations located in the limnetic zone of Pedu reservoir.The zooplankton community was dominated by rotifers (11 species),followed by cladocerans (9 species) and copepods (2 species).Four species of zooplankton comprised of 3 rotifers,Brachionus quadridentata,Brachionus caudatus and Keratella cochlearis and one cladoceran,Ceriodaphnia cornuta were present at all sampling stations.Species richness was highest at Station 2 (17 species) followed by Station 4 and Station 8 (14 species),Station 5 (15 species),Station 7 (11 species),Station 6 (10 species),Station 3 (9 species) and Station 1 (7 species).With an exception of water transparency,all other water quality parameters such as temperature,dissolved oxygen,conductivity,pH and total dissolved solids were not significant when compared between sampling stations.The study found that station 5 which was located in a calm strait,protected from strong wave and wind was a suitable area for zooplankton growth and establishment.Factors supporting the findings included highest water transparency (3.4 m),rich in species numbers (15 species),high diversity index (0.950) and evenness index (0.808).  相似文献   

Improved stove programs need robust methods to estimate carbon offsets     

Michael Johnson  Rufus Edwards  Omar Masera 《Climatic change》2010,102(3-4):641-649

Current standard methods result in significant discrepancies in carbon offset accounting compared to approaches based on representative community based subsamples, which provide more realistic assessments at reasonable cost. Perhaps more critically, neither of the currently approved methods incorporates uncertainties inherent in estimates of emission factors or non-renewable fuel usage (fNRB). Since emission factors and fNRB contribute 25% and 47%, respectively, to the overall uncertainty in offset estimates for Purépecha communities in Mexico, exclusion of this uncertainty is a critical omission. When the recommended uncertainty for default emission factors and the uncertainty associated with regional estimates of fNRB are included the lower 95% confidence intervals of both Clean Development Mechanism and Gold Standard methods exceed the total amount of carbon saved, which would result in zero marketable carbon savings if approaches recommended by the IPCC Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories, or Land use, Land-Use Change and Forestry (LULUCF) are to be followed. In contrast, for the same communities, methods using representative subsamples of emission factors and fuel consumption, combined with community-level fNRB estimates, result in significant carbon offsets with a lower 95% confidence interval of 2.3 tCO₂e home^???1 year^???1. Given the misleading estimates, revision of the currently approved methodologies to provide robust estimates of carbon offsets is strongly recommended.  相似文献   

Food web structure of sandy beaches: Temporal and spatial variation using stable isotope analysis     

Leandro Bergamino  Diego Lercari  Omar Defeo 《Estuarine, Coastal and Shelf Science》2011,91(4):2751

  相似文献   

The bearing capacity of surface strip foundations on geogrid-reinforced sand and clay — a comparative study   总被引：3，自引：0，他引：3  

B. M. Das  E. C. Shin  M. T. Omar 《Geotechnical and Geological Engineering》1994,12(1):1-14

Summary Laboratory model test results for the ultimate bearing capacity of a strip foundation supported by geogrid-reinforced sand and saturated clay are presented. One type of geogrid only was used for all the tests. On the basis of the model test results, the optimum depth and width of reinforcing layers and the optimum depth of the location of the first layer of the geogrid in sand and saturated clay were determined and compared.  相似文献