Sedimentary Basins in the Western White Nile, Sudan, as Indicated by a Gravity Survey

An academic geophysical research as a regional gravity survey was made during 1994 in the Western White Nile to infer the shallow crustal structures in the area. The result of the survey was compiled as a Bouguer anomaly map with a contour interval of 2 ×10-5m/s2. It is found that the negative residual anomalies are related to the Upper Cretaceous sediments (Nubian Sandstone Formation) filling all depressions in the Basement complex surface while the positive residual anomalies are attributed to the relatively shallow or outcropping Basement rocks and the steep gravity gradients are resulting from the sharp contacts between the sedimentary infill and the Basement rocks. To define the geological structures in the area, 9 profiles were studied. For each of the profiles, measured and computed Bouguer gravity anomalies, crustal density model, subsurface geology evaluation were performed. A G-model computer program was applied in the gravity modeling, which is based on the line-integral method of gravity computation. A geological/structural map was proposed showing inferred sedimentary basins, faulting troughs and uplifted Basement block and tectonic trends. The basins are believed to be fault-controlled which developed by extensional tectonics (pull-apart mechanism). As for the mechanism and cause of faulting, the area is considered as a part of the Central Sudan rift system which had been subjected to several tectonic events since Early Cambrian to Tertiary times which resulted in the formation of several fracture systems associated with block subsidence, rifting and basin formation.     

Assessment of crushed shales for use as compacted landfill liners

The possibility of using crushed shales as landfill liners is investigated in this study. Two types of shales were studied by performing the following laboratory tests: hydraulic conductivity, compaction, swelling, consolidation, X-ray diffraction (XRD), scanning electron microscope (SEM) and chemical analysis. For both compacted shales, the hydraulic conductivity was in order of 10^− 7 cm/s or less which satisfies the specifications for landfill liners. The results of XRD and SEM support the low values of the hydraulic conductivity. Because of the dominant presence of low-activity kaolinite, there was no significant change in the hydraulic conductivity when the compacted shales are exposed to calcium chloride solution. The compressibility of the compacted clay was low and no serious post-construction settlement is expected. The shear strength of the compacted shales was within the usual expected range for earthen liners and, therefore, should pose no challenges with respect to shear strength. The crushed shales also satisfy the other criteria related to Atterberg limits and grain size.     

Seismic reflection imaging of active faults and their tectonic behavior in the Northern Moroccan margin. Is the Nekor fault a pure strike-slip fault?

The study of 1000-km seismic reflection profiles, along the Northern Moroccan margin, allowed browsing new imaging in detail about the regional geological structures and their functioning. To achieve this goal, we elaborated a high-resolution depth model and a global tectonic sketch. The influence of recent tectonic activity is manifested by normal and strike-slip faults, trending mainly 70° N and 125° N. In this segment, the Nekor strike-slip fault seems to be connected to a secondary major fault system that changes direction from 30° N to 70° N, and changing behavior to left-lateral strike-slip fault with normal component. Analysis of local seismic activity recorded from 1990 to 2014 with moderate magnitudes activity shows alignments in clear superposition with the detected active faults in seismic reflection lines.     

Groundwater management scenarios for the Biyadh-Wasia aquifer systems in the eastern part of Riyadh region,Saudi Arabia

Groundwater stored in the deep seated sedimentary aquifers is the most important source of water supply. The lack of sufficient groundwater recharge and the overdependence on groundwater might lead to unavailability of this precious natural resource if proper management practices are not adopted. Finite difference modelling using the MODFLOW program was carried out in the east of Riyadh city to simulate the groundwater level conditions under different abstraction scenarios. The simulated aquifer system combines the Wasia and Biyadh aquifer (composed of sandstone) and Aruma aquifer (limestone) which lies between 24°30'00"- 25°30'00" N and longitudes 47°00'00"- 48°00'00"E. The transmissivity and storage coefficient values of Biyadh aquifer are 7.0x10^-3 to 7.0x10^-2 m²/day and 3.7x10^-4 to 9.4x10^-4 respectively. The transmissivity and storage coefficient values of Wasia aquifer ranges from 6.7x10^-3 to 8.5x10^-2 m²/day and 2x10^-4 to 2.3x10^-4 respectively. The model calibration involved altering the values of model input parameters to match field conditions within certain acceptable limits to forecast the aquifer response over a period of 35 years (2015-2050). The modelling grid consisted of 20 and 24 columns with the grids spacing of 4 km for the small grids and 6 km for large grids. The results showed that though the Wasia aquifer was productive, it showed a large decline in water levels if water abstraction continued at the present rate. If the existing trends of groundwater withdraw continues; the piezometric heads in Wasia and Biyadh aquifers will decline by the year 2050. A reduction in 25% of the existing groundwater pumping rate in the well field will minimize the rate of groundwater decline in the aquifer to a considerable extent.     

Dynamic simulation of beam-like structure with a crack subjected to a random moving mass oscillator

In this paper,dynamic simulation of a beam-like structure with a transverse open crack subjected to a random moving mass oscillator is investigated.The simultaneous effect of a crack and a random oscillator has not been addressed up to now.The crack in the beam at different locations and with different depths is considered as one group of damage,each as an individual imperfection.In addition,bearing immobility is considered as another type of problem in the beam.Mass, stiffness,damping and velocity of th...     

Laboratory experiments on three-dimensional deformable granular landslides on planar and conical slopes

Landslides of subaerial and submarine origin may generate tsunamis with locally extreme amplitudes and runup. While the landslides themselves are dangerous, the hazards are compounded by the generation of tsunamis along coastlines, in enclosed water bodies, and off continental shelves and islands. Tsunamis generated by three-dimensional deformable granular landslides were studied on planar and conical hill slopes in the three-dimensional NEES tsunami wave basin at Oregon State University based on the generalized Froude similarity. A unique pneumatic landslide tsunami generator (LTG) was deployed to control the kinematics and acceleration of the naturally rounded river gravel and cobble landslides to simulate broad ranges of landslide shapes and velocities along the slope. Lateral and overhead cameras are used to measure the landslide shapes and kinematics, while acoustic transducers provide the shape of the subaqueous deposits. The subaerial landslide shape is extracted from the camera images as the landslide propagates under gravity down the hill slope, and surface reconstruction of the landslide is conducted using the stereo particle image velocimetry (PIV) system on the conical hill slope. Subaerial landslide surface velocities are measured with a planar PIV system on the planar hill slope and stereo PIV system on the conical hill slope. The submarine deposits are characterized by the runout distances and the deposit thickness distributions. Larger cobbles are observed producing hummock type features near the maximum runout length. These unique laboratory landslide experiments serve to validate deformable landslide models as well as provide the source characteristics for tsunami generation.     

On the recent global mean sea level changes: Trend extraction and El Niño's impact

The spatial sampling offered by TOPEX and Jason series of satellite radar altimeters and its continuity during the last twenty years are major assets to provide an improved vision of the global mean sea level (GMSL). The objective of this paper is to examine the recent GMSL variations (1993–2012) and to investigate the correlation between the GMSL and ENSO (El Niño-southern oscillation) episodes. For this purpose, a mean sea level anomalies time series, obtained from TOPEX, Jason-1 and Jason-2 measurements, is used to determine the trend of GMSL changes by using a simplified form of an unobserved components model (namely UCM). Then, to investigate the impact of the ENSO phenomenon on the GMSL changes, we considered the sea surface temperature anomalies (SSTA) index over the Niño3 region (5N–5S 150W–90W). Cross wavelet transform and wavelet coherence analysis are performed to expose common power between the GMSL changes and the SSTA index and their relative phase in the time–frequency space. The results indicate that there are in the estimated GMSL's trend a number of fluctuations over short periods that are least partly related to the El Niño/La Niña episodes. Cross wavelet transform and wavelet coherence analysis indicate that a significant correlation between GMSL and ENSO occurred during 1997–1998, 2006–2007, 2009–2010 El Niño events and 2007–2008 and 2010–2011 La Niña ones. All these areas show in-phase relationship, suggesting that GMSL and SSTA index vary synchronously.     

Wind Regimes Windward of a Shelterbelt Protecting Gravity Irrigated Crop Land from Moving Sand in the Gezira Scheme (Sudan)

Summary  The work reported on was part of a more comprehensive study dealing with threatening sand movement towards the northwestern part of the Gezira irrigation scheme, Sudan. An irrigated sand blocking shelterbelt Eucalyptus microtheca is used to prevent canals and gravity irrigated crop land to be further affected. The objective of this paper is to report on the wind data that were obtained, mainly windward of this belt, and to deal with their implications and those of the belt characteristics and deposited sand in interaction with the wind for combating local sand movements and further desertification. Outside the influence of the belt, wind speed over eroded land was increasingly higher than that over irrigated land with the growth of cotton. Both these values were considerably higher than those reported from the nearest meteorological stations. The two prevailing winds, of which the summer SW wind was perpendicular to the belt, had consistent annual patterns during three years of observation. Also the diurnal patterns were very reproducible. Wind speed within the belt, at 1 m height, showed fast reduction inwards above the deposited sand. Efforts to control moving sand in the source area should be joined with those made at the borders of agricultural land. Received August 20, 1997 Revised September 30, 1998     

Thermal metamorphism of primitive meteorites—I. Variation of six trace elements in Allende carbonaceous chondrite heated at 400–1000°C

Determination by neutron activation of 6 trace elements retained in Allende (C3) samples heated at 400–1000°C for 1 week in a low-pressure (initially ~10^?5 atm H₂) atmosphere reveals loss of small proportions of Ga and Se and large proportions of Bi, In and Tl-Co being unaffected. The retentivity patterns for the 5 volatile elements differ and in no way duplicate a step-function. In contrast to these trace elements, sulfur is initially present in discrete mineral(s) and visually it appears to be released over a narrow temperature range. Elements are lost more easily from powder than from chips but the difference is ≤35 per cent. Above 600°C, the process of loss appears due to process(es) with apparent activation energies of 2 kcal/mole (Bi, Tl), 4 kcal/mole (Se) and 22 kcal/mole (In). Loss of Bi, Se and Tl below 600°C involves higher apparent activation energies. Two-element correlation diagrams involving Bi, In and Tl are consistent with the idea that trends among highly-volatile elements in enstatite chondrites arise from metamorphism.     

Development implications of demographic trends and projections for an arid region:: the case of the Badia Research and Development Project area of Jordan

Development planners in arid areas face many difficulties in preparing appropriate strategies. Their task is made harder by the dearth of reliable demographic information. This paper presents population projections for the arid area of eastern Jordan covered by the Badia Research and Development Project and evaluates the economic and social implications of these projections over the next 20 years. The paper argues that conventional demographic forecasting methods are extremely problematic when applied to a population such as this. Furthermore, the pastoral economy, which has in the past been the main source of livelihood, cannot hope to sustain the region's future population. High fertility rates will continue to place great stress on the educational and health infrastructure. If appropriate planning responses are not achieved, the demographic regime of the Badia project area and the quality of life of the population may continue to diverge from the patterns found in other parts of Jordan.