Nature and geochemistry of surface sediments of the mangrove environment along the Egyptian Red Sea coast

Grain size and geochemical analyses have been carried out on 58 samples collected from different areas of mangrove environment of the Egyptian Red Sea coast. The texture characteristics of mangrove sediments show that the mean size decreases in sediments of coastal areas while increase in island sediments and the sediment type generally changes from sand to slightly gravelly muddy sand. The sediments are composed mainly of poorly sorted, negatively nearly symmetrical and leptokurtic fine sands. Cluster analysis showed that, distribution of gravel, sand and mud fractions is related to bottom facies and type of sediment source. Generally, sand fraction is the main category among the three constituents. Geochemically the factor controlling the carbonate content of studied sediments includes material supply of biogenic and terrigenous components. Therefore, sediments of Hamata area, km 17 south Safaga, Wadi El-Gemal Island and Abu-Minqar Island are terrigenous sediments, while sediments of km 37 north Quseir are highly carbonates. In general organic matter is higher in the mangrove sediments relative to adjacent areas. The high organic matter in the mangrove sediments is primarily due to the high supply from primary productivity, terrestrial and reworked sediments. Texture is the main controlling factor for the organic matter enrichment. Spatial variations in the phosphorus content in the different studied localities are related to the sources of phosphorus to the area. In comparison, cluster analysis indicates that phosphorus might be transported from terrestrial source to the sea through wadis draining the excavated Upper Cretaceous phosphate rocks. Also, the abundance of phosphorus content may be attributed to phosphatization of calcareous skeletons. Our observations provide knowledge on the physico-chemical effects and will be useful in the management and suitable development of the areas under study. In addition it represent database in the future.     

The response of the upper ocean to tropical cyclone Viyaru over the Bay of Bengal

Better forecast of tropical cyclone(TC) can help to reduce risk and enhance management. The TC forecast depends on the scientific understanding of oceanic processes, air-sea interaction and finally, the atmospheric process. The TC Viyaru is taken as an example, which is formed at the end of 11 May 2013 and sustains up to 17 May 2013 during pre-monsoon season. Argo data are used to investigate ocean response processes by comparing pre-and post-conditions of the TC. Eight oceanic parameters including the sea surface temperature(SST), the sea surface salinity(SSS), and the barrier layer thickness(BLT), the 26°C isotherm depth in the ocean(D26), the isothermal layer depth(ILD), the mixed layer depth(MLD), the tropical cyclone heat potential(TCHP) and the effective oceanic layer for cyclogenesis(EOLC) are chosen to evaluate the pre-and post-conditions of the TC along the track of Viyaru. The values of the SST, D26, BLT, TCHP and EOLC in the pre-cyclonic condition are higher than the post-cyclonic condition, while the SSS, ILD and MLD in the post-cyclonic condition are higher than the pre-cyclonic condition of the ocean due to strong cyclonic winds and subsurface upwelling. It is interesting that the strong intensity of the TC reduces less SST and vice versa. The satisfied real time Argo data is not available in the northern Bay of Bengal especially in the coastal region. A weather research and forecasting model is employed to hindcast the track of Viyaru, and the satellite data from the National Center Environmental Prediction are used to assess the hindcast.     

Cyclone Gonu storm surge in Oman

Super Cyclone Gonu is the strongest tropical cyclone on record in the Arabian Sea. Gonu caused coastal damage due to storm surge and storm wave impact as well as wadi flooding. High water marks, overland flow depths, and inundation distances were measured in the coastal flood zones along the Gulf of Oman from 1 to 4 August 2007. The high water marks peaked at Ras al-Hadd at the eastern tip of Oman exceeding 5 m. The storm surge of Gonu is modeled using the Advanced Circulation Model (ADCIRC). The multi-hazard aspect is analyzed by comparing observations from Cyclone Gonu with the 2004 Indian Ocean Tsunami.     

Subsidies to high seas bottom trawl fleets and the sustainability of deep-sea demersal fish stocks

The life spans of demersal species of fishes occurring in deep-waters are much longer and their potential growth rates much lower than those of related shallow water species. As a result, deep-sea demersal fish species are more vulnerable to exploitation. This is because low growth rates relative to the available market discount rate for capital makes it desirable for fishing firms to mine, rather than sustainably exploit, these resources even in the absence of fisheries subsidies. However, it is common knowledge that governments around the world do provide subsidies to their fishing industries. The objective of this contribution is to estimate the global amount of subsidies paid to bottom trawl fleets operating in the high seas, i.e., outside of the Exclusive Economic Zones of maritime countries. Our study suggests that fisheries subsidies to these fleets stand at about US$152 million per year, which constitutes 25% of the total landed value of the fleet. Economic data for bottom trawlers suggest that the profit achieved by this vessel group is normally not more than 10% of landed value. The implication of this finding is that without subsidies, the bulk of the world's bottom trawl fleet operating in the high seas will be operating at a loss, and unable to fish, thereby reducing the current threat to deep-sea and high seas fish stocks.     

Study of the 26 December 2011 Aswan earthquake,Aswan area,South of Egypt

The source process and parameters for a moderate earthquake of magnitude Ml 4.1 that occurred on the Kalabsha fault at the Aswan area are analyzed. The derived focal mechanisms of this event and other two aftershocks using polarities of P, SV, and SH waves show strike-slip fault with minor vertical movement of normal type. The solutions give two nodal planes trending ENE–WSW and NNW–SSE in close agreement with the surface traces of the faults crossing the area. The movement is right lateral along the first plane while left lateral along the second one. The rupture process characterization of this event has been investigated by using the empirical Green’s function deconvolution method. By inversion only for the P wave part of the records of these three events (main and other two aftershocks), the source time function for the master events and the azimuthally variations in the (RSTF) pulse amplitude are retrieved for estimating the rupture directivities. The estimated rupture direction is combined with the P-wave focal mechanisms for the three events to identify the fault plane solution for these earthquakes. Based on the width, amplitudes, and numbers of the isolated source time functions, a complex bi-lateral rupture of the studied earthquake is delineated. The source parameters of the master event is calculated and the derived corner frequencies f _o for P-wave spectra show a value of 6.6 Hz; the seismic moment (M _o ) is 4.2?×?10²² Nm; the average displacement (U) is 0.5 m; fault radius (r) 40 m; the average value of the stress drops (Δσ) is 0.6 Mpa, and the moment magnitude (M _w ) is 4.4.     

Investigation of a relation between radiogenic heat production and kinetic surface temperature from multispectral ASTER-TIR data: a case study on Elmissikat-Eleridiya granites,Central Eastern Desert,Egypt

In this paper, an attempt was tried to study the relation between radiogenic heat production rate (RHPR) that derived from gamma-ray spectrometric data and the kinetic surface temperature KST, which was calculated from the thermal emission and reflection radiometer-thermal infrared (ASTER-TIR) imagery applied on Elmissikat-Eleridiya district. This area is considered one of the most important uranium localities in the Central Eastern Desert of Egypt. The gamma-ray spectrometric data including both airborne data and in situ measurements concurrent with the collection of 20 rock samples were used to determine the rock density. The ground gamma-ray spectrometry has been conducted using GS-256 spectrometer at the same locations of rock samples. The gamma-ray spectrometric data (airborne and ground) beside rock density data were used for calculating RHPR. Alongside, pairs of daytime and nighttime ASTER-TIR images were collected and surface kinetic temperature for both day (daytime kinetic surface temperature (DKST)) and night (nighttime kinetic surface temperature (NKST)) were derived by using reference channel emissivity technique. The study showed a relative higher RHPR within syenogranite (4.2 up to 6 μW/m³) than other rock units. Besides, the KST of syenogranite ranged from 33 to 48 °C in daytime and between 7 and 17 °C at night. Comparing all results, no clear relation between RHPR and KST is evident. This is due to the very weak RHPR that is not sufficient to affect the surface heat temperature, which can be remotely sensed by ASTER satellite TIR data. This factor in addition to other factors such as: structural elements, topography, geographic locations, shading and scattering, rock moisture and density, can strongly affect the surface temperature. In conclusion, these results could be improved in areas of very high radioelement concentrations, especially ²³⁵U and through the use of the enhanced spatial resolution of future satellite TIR imaging instruments.     

GeoNDT: a fast general-purpose computational tool for geotechnical non-destructive testing applications

The non-destructive testing (NDT) plays a crucial role in geotechnical engineering and geophysical applications, especially in the design of earthquake-resistant foundations, geotechnical field investigation, and material characterization and detection of underground anomaly. Currently, the existing signal interpretation methods in NDT measurements still predominantly rely on empirical relations or subjective judgements. In this paper, we present the GeoNDT software, which is developed to provide an advanced physics-based signal interpretation method for NDT characterization of multiphase geomaterials. GeoNDT is able to model the propagation of stress waves and dispersion relations in dry (elastodynamic), saturated (two-phase poroelastodynamic), and three-phase frozen (multiphase poroelastodynamic) geomaterials using the meshless spectral element method. GeoNDT is flexible, general-purpose, and can be used seamlessly for advanced signal interpretation in geophysical laboratory testing including the bender element and ultrasonic pulse velocity tests, characterization of complex multiphase geomaterials, and in situ shallow seismic geophysics including the falling weight deflectometer and multichannel analysis of surface waves tests. The advanced physics-based signal interpretation feature of GeoNDT allows the quantitative characterization of geophysical and geomechanical properties of geomaterials and multilayered geosystems independently without making any simplified assumptions as common in the current practice.

     

印度河扇水道堤岸外侧更新世沉积物波发育特征与形成过程分析*

印度河扇更新世发育的沉积物波结构复杂、形态多样,其形成过程的认识程度低。本次研究通过高分辨率地震数据和地震解释技术,研究了印度河扇沉积物波的波长、形态、波峰变化等形态特征;阐述了沉积物波与沉积物变形特征的差异、识别了两者的区分标志;总结了水道堤岸斜坡和区域斜坡上沉积物波的分布规律;在此基础上,讨论了沉积物波的形成机理和控制因素,分析了沉积物波的形成过程,并建立了印度河扇沉积物波的形成模式。研究表明: (1)研究区沉积物波波长平均为486.84 m,最大1473 m;波高在10~60 m之间,平均30 m。(2)沉积物波的形态有对称型和非对称型,其迁移方式有上坡迁移型、加积型和下坡迁移型;沉积物波主要发育在水道堤岸的斜坡上,在区域斜坡上也发育少量的沉积物波,这2种沉积物波波脊的走向差异很大,水道堤岸斜坡上的沉积物波主要分布于水道凹岸堤岸的外侧,距离水道越远其规模(波长、波高)越小,波脊走向近于NE-SW方向,与水道的走向平行或斜交;区域斜坡上的沉积物波波脊的走向多为NW-SE向,平行于区域斜坡的走向,离源区越远规模越大。(3)水道堤岸斜坡上的沉积物波是由水道型浊流在离心力的作用下,溢出水道的凹岸,在堤岸外侧的斜坡上沉积形成的,堤岸斜坡的角度对沉积物波的发育规模影响不大,浊流的强度和输沙量对其规模影响大;区域斜坡上发育的沉积物波是由顺坡而下的非水道化的浊流沉积形成;滑塌变形造成的起伏地貌以及早期沉积物波的存在,也都影响了后期沉积物波的发育。     

Inferring the chemical parameters for the dissolution of fluoride in groundwater

Geochemical study of groundwater from 58 selected fluoride-rich areas in different parts of India that includes eight states indicates that: 1. These groundwaters are alkaline in pH (7.4-8.8) and their electrical conductivity varies from 530-2,680 µS/cm and fluoride concentration from 1.7-6.1 mg/l. Presence of fluoride-bearing minerals in the host rocks and their interaction with water is considered to be the main cause for fluoride in groundwater. 2. The decomposition, dissociation and dissolution are the main chemical processes for the occurrence of fluoride in groundwater. During rock-water interaction, concentration of fluoride in rock, aqueous ionic species and residence time of interaction, etc. are also important parameters. 3. This study indicates that 85% groundwater samples have EC: 1,000-2,000 µS/cm, pH: 7.5-8.5, and HCO₃/Ca (epm ratio): 0.8-2.3. 4. The Ca and HCO₃ contents of groundwater samples have shown good correlation with fluoride.     

Environmental risk assessment of some potentially toxic elements in El-Tabbin region (Cairo, Egypt)

As much as 24 soil samples and 6 stream sediments from the River Nile were studied in El-Tabbin region (Great Cairo, Egypt). Twelve chemicals, potentially toxic elements posing potential environmental risk, were the object of concern in this study. Mean contents of analysed elements (in mg kg^?1) in soils and the River Nile stream sediments were the following: As_s 3.6/As_ss 1.5, Cd_s 0.33/Cd_ss 0.12, Cr_s 87.7/Cr_ss 141.5, Cu_s 40.3/Cu_ss 43.8, Hg_s 0.03/Hg_ss 0.13, Pb_s 33.3/Pb_ss 20.2, Zn_s 150/Zn_ss 109, Se_s 0.24/Se_ss 0.05, Ni_s 37.2/Ni_ss 48, Sb_s 1.25/Sb_ss 1, Ba_s 892/Ba_ss 431, V_s 103.3/V_ss 167.8. Furthermore, geochemical background values were derived for soil and stream sediment samples. The values are as follows (in mg kg^?1): As_s 1.33/As_ss 1, Cd_s 0.48/Cd_ss 0.05, Cr_s 54.7/Cr_ss 106.5, Cu_s 23.8/Cu_ss 23, Hg_s 0.025/Hg_ss 0.095, Pb_s 15.3/Pb_ss 13.5, Zn_s 70/Zn_ss 55, Se_s 0.13/Se_ss 0.05, Ni_s 19.5/Ni_ss 32.5, Sb_s 1/Sb_ss 1, Ba_s 266/Ba_ss 275, V_s 50.7/V_ss 119. More than two-thirds of soil and sediment samples exceeded established (based on literature data) risk limit values for non-polluted environment. Based on environmental risk assessment for potentially toxic elements in soils and sediments in more than 45% of total area disturbed environment (I _ER = 1–3) was documented and more than 13% of territory was characterised with highly disturbed environment (I _ER > 3).