Crustal structure of northern Egypt from joint inversion of receiver functions and surface wave dispersion velocities

In this study, we used a combined inversion of body wave receiver functions and surface wave dispersion measurements to provide constraints on the crustal structure of northern Egypt. The two techniques are complementary to each other: receiver functions (RFs) are sensitive to shear-wave velocity contrasts, while surface wave dispersion (SWD) measurements are sensitive to finite variations of shear-wave velocity with depth. A database of 122 teleseismic events digitally recorded by the Egyptian National Seismological Network (ENSN) stations has been used as well. To enhance the resulting RFs at each ENSN station, the H-k stacking method was applied. A joint inversion process between the resulting receiver functions and the surface wave dispersion curves was applied as well. We have produced three averaged velocity structure models for distinct geographic and tectonic provinces namely Sinai, eastern desert, and western desert from east to the west respectively. These models will deeply help in estimation the epicenter distance of earthquake, focal mechanism solutions, and earthquake hazard analysis in northern Egypt. An obvious image of the subsurface structure has been determined which shows that generally the crustal structure of northern Egypt consists of three layers covered with a sequence of sediments that differs in thickness from across the region except in the Sharm area where the sedimentary cover is absent. The obtained results indicate that crustal thickness differs from east to west and reaches its maximum value of about 36 km at Siwa station (SWA) in the western desert and its minimum value of about 28 km at Sharm station (SHR) of the southern tip of the Sinai Peninsula. The Vp/Vs ratio varies between 1.71 and 2.07 in northern Egypt. Generally, the high values (1.93) of (Vp/Vs) at SWA station may reflect the well-known rich aquifer with fully saturated sediments of the Swia Oasis in the Western Desert. Moreover, the highest value (2.07) of (Vp/Vs) at BNS station may be attributed to the widespread recently discovered hydrocarbon fields at the Beni-Suef Basin along the Eastern Desert. Finally, an integrated geophysical and hydrological study of the dimensions and physical properties of the aquifer and hydrocarbon fields at SWA and BNS stations to confirm if they are sufficient to produce the elevated Vp/Vs ratios or not become essential and highly recommended.     

Characterizing the active tectonics in the Oran region (Algeria) and recasting the 1790 earthquake

In this work, we reappraise the seismogenic potential of the geologic structures in the western Tell Atlas of Algeria, considered active host to moderate to low magnitude earthquakes. The direct identification of active faults is generally a difficult task in northern Algeria. The active tectonics in the Oran Plio-Quaternary age basin (Northwestern Algeria) is analyzed and characterized through a morpho-structural study combining topographic, geomorphologic, geological, and neotectonic data. Folds and fault scarps affecting Quaternary deposits show that the region is affected by compressional deformation still active nowadays, as shown by the recorded seismic activity. Our new observations enable a better understanding of the present seismotectonic context of the Oran region, particularly with regard to the magnitude and source of the 1790 Oran damaging event. The obtained result helps to shed some light on the elusive active tectonics characterizing this coastal area, and to assess regional seismic hazard, particularly in coastal zones where large seismogenic areas straddle the onshore–offshore zones.     

Exploring Groundwater Resources and Recharge Potentialities at El-Gallaba Plain,Western Desert,Egypt

Egypt has a fast-growing population rate of 2.5%/year; consequently, there is an increase in the water demand for living and launching different development plans. Meanwhile, there is intensive construction of several dams in the upstream Nile basin countries. Thus, it is necessary to search for new water resources to overcome the expected shortages of the Nile water supply by focusing on alternative groundwater resources. El-Gallaba Plain area is one of the most promising areas in the western desert of Egypt attaining the priority for new reclamation projects; however, its hydrogeological setting is not well understood. The present work aims at identifying the recharge potential of the groundwater aquifers in El-Gallaba Plain, as well as exploring the role of geologic structures as natural conduits, and evaluating the groundwater types, origin and distribution. The integration of hydrogeophysical studies (aero and land magnetic surveys, vertical electrical sounding), hydrochemical analyses and remote sensing were successfully used for assessing the groundwater development potential. The hydrogeophysical studies show a large graben bound aquifer with thickness exceeding 220 m. The hydrochemical results indicate the presence of three major water types; Na mix, Na Cl, Na Cl HCO₃ with salinities ranging between 227 and 4324 mg/L. The aquifer receives little recharge from the western fractured calcareous plateau from past pluvial periods and scarce present flashfloods. There is no indication for recent recharge from Lake Nasser to the aquifer domain. Further modeling studies are essential for establishing sustainable abstraction levels from this aquifer.     

The role of ground motion duration and pulse effects in the collapse of ductile systems

The seismic collapse capacity of ductile single-degree-of-freedom systems vulnerable to P-Δ effects is investigated by examining the respective influence of ground motion duration and acceleration pulses. The main objective is to provide simple relationships for predicting the duration-dependent collapse capacity of modern ductile systems. A novel procedure is proposed for modifying spectrally equivalent records, such that they are also equivalent in terms of pulses. The effect of duration is firstly assessed, without accounting for pulses, by assembling 101 pairs of long and short records with equivalent spectral response. The systems considered exhibit a trilinear backbone curve with an elastic, hardening and negative stiffness segment. The parameters investigated include the period, negative stiffness slope, ductility and strain hardening, for both bilinear and pinching hysteretic models. Incremental dynamic analysis is employed to determine collapse capacities and derive design collapse capacity spectra. It is shown that up to 60% reduction in collapse capacity can occur due to duration effects for flexible bilinear systems subjected to low levels of P-Δ. A comparative evaluation of intensity measures that account for spectral shape, duration or pulses, is also presented. The influence of pulses, quantified through incremental velocity, is then explicitly considered to modify the long records, such that their pulse distribution matches that of their short spectrally equivalent counterparts. The results show the need to account for pulse effects in order to achieve unbiased estimation of the role of duration in flexible ductile systems, as it can influence the duration-induced reduction in collapse capacity by more than 20%.     

Integrated core-log interpretation of Wenchuan earthquake Fault Scientific Drilling project borehole 4 (WFSD-4)

Understanding slip behavior of active fault is a fundamental problem in earthquake investigations. Well logs and cores data provide direct information of physical properties of the fault zones at depth. The geological exploration of the Wenchuan earthquake Scientific Fault drilling project (WFSD) targeted the Yingxiu-Beichuan fault and the Guanxian Anxian fault, respectively. Five boreholes (WFSD-1, WFSD-2, WFSD-3P WFSD-3 and WFSD-4) were drilled and logged with geophysical tools developed for the use in petroleum industry. WFSD-1, WFSD-2 and WFSD-3 in situ logging data have been reported and investigated by geoscientists. Here we present for the first time, the integrated core-log studies in the Northern segment of Yingxiu-Beichuan fault (WFSD-4) thereby characterizing the physical properties of the lithologies(original rocks), fault rocks and the presumed slip zone associated with the Wenchuan earthquake. We also present results from the comparison of WFSD-4 to those obtained from WFSD-1, WFSD-3 and other drilling hole in active faults. This study show that integrated core-log study would help in understanding the slip behavior of active fault.     

Development of a vector-based 3D grain entrainment model with application to X-ray computed tomography scanned riverbed sediment

Sediment transport equations typically produce transport rates that are biased by orders of magnitude. A causal component of this inaccuracy is the inability to represent complex grain-scale interactions controlling entrainment. Grain-scale incipient motion has long been modelled using geometric relationships based on simplified particle geometry and two-dimensional (2D) force or moment balances. However, this approach neglects many complexities of real grains, including grain shape, cohesion and the angle of entrainment relative to flow direction. To better represent this complexity, we develop the first vector-based, fully three-dimensional (3D) grain rotation entrainment model that can be used to resolve any entrainment formulation in 3D, and which also includes the effect of matrix cohesion. To apply this model we use X-ray computed tomography to quantify the 3D structure of water-worked river grains. We compare our 3D model results with those derived from application of a 2D entrainment model. We find that the 2D approach produces estimates of dimensionless critical shear stress ( ) that are an order of magnitude lower than our 3D model. We demonstrate that it is more appropriate to use the c-axis when calculating 2D projections, which increases values of to more closely match our 3D estimates. The 3D model reveals that the main controls on critical shear stress in our samples are projection of grains, cohesive effects from a fine-grained matrix, and bearing angle for the plane of rotation (the lateral angle of departure from downstream flow that, in part, defines the grain's direction of pivot about an axis formed by two contact points in 3D). The structural precision of our 3D model demonstrates sources of geometric error inherent in 2D models. By improving flow properties to better replicate local hydraulics in our 3D model, entrainment modelling of scanned riverbed grains has the potential for benchmarking 2D model enhancements. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.     

Chemometric Differentiation of Oil Families and Their Potential Source Rocks in the Gulf of Suez

Natural Resources Research - An oil–oil and oil–source rock correlation study was carried out using chemometric methods applied to geochemical data for 123 Upper Cretaceous—Lower...     

Improving Adaptive Neuro-Fuzzy Inference System Based on a Modified Salp Swarm Algorithm Using Genetic Algorithm to Forecast Crude Oil Price

Natural Resources Research - This paper presents a novel forecasting model for crude oil price which has the largest effect on economies and countries. The proposed method depends on improving the...     

Optical and near-infrared photometric study of NGC 6724

BVRI CCD photometry of the poorly studied open cluster NGC 6724 has been carried out down to a limiting magnitude of V ～20 mag. The stars of the cluster have been observed using the Newtonian focus(f/4.84) of the 74-inch telescope at Kottamia Astronomical Observatory in Egypt.Also, the 2 MASS-JHK system is used to confirm the results we obtained. The main photometric parameters have been estimated for the present object; the diameter is found to be 6 arcmin, the distance is 1530±60 pc from the Sun and the age is 900±50 Myr. The optical reddening E(B-V) = 0.65 mag,while the infrared reddening is E(J-H) = 0.20 mag. The slope of the mass function distribution and the relaxation time estimations indicate that cluster NGC 6724 is dynamically relaxed.     

A stable flat universe with variable cosmological constant in f(R,T) gravity

In this paper, a general FRW cosmological model has been constructed in f(R,T) gravity reconstruction with variable cosmological constant. A number of solutions to the field equations has been generated by utilizing a form for the Hubble parameter that leads to Berman's law of constant deceleration parameter q = m-1. The possible decelerating and accelerating solutions have been investigated. For(q 0) we get a stable flat decelerating radiation-dominated universe at q = 1. For(q 0) we get a stable accelerating solution describing a flat universe with positive energy density and negative cosmological constant. Nonconventional mechanisms that are expected to address the late-time acceleration with negative cosmological constant have been discussed.