Seismic hazard assessment and rheological implications: a case study selected for cities of Saudi Arabia along the eastern coast of Red Sea

A probabilistic approach is used to evaluate the seismic hazard for 12 strategic cities in Saudi Arabia along the eastern coast of Red Sea. The focal depth variations controlled by rheological characteristics are taken into account for hazard calculations, and its creditability is tested through sensitivity analysis for hazard results. This study presents a neo-probabilistic seismic hazard assessment methodology in which the focal depth distribution of earthquakes within seismogenic layer is divided into three depth slices. These depth slices are based upon rheological characteristic of seismogenic layer. The hazard results are obtained using this depth-slice methodology and conventional approach in which uniform distribution of seismicity within seismogenic layer is assumed. The sensitivity analysis culminated in underestimation of hazard values in higher frequencies for uniform distribution of seismicity within seismogenic layer. Foregoing the observations recorded above, it can be concluded that the exploitation of depth-slices biased by the rheology to calculate hazard is relatively preferable in the situations demanding safety measures.     

A Raman spectroscopic investigation of Fe-rich sphalerite: effect of fe-substitution

A Raman spectroscopic study of Fe-rich sphalerite (Zn_{1 − x} Fe _x S) has been carried out for six samples with 0.10 ≤ x ≤ 0.24. Both the intensities and frequencies of the TO and LO modes of sphalerite are approximately independent of Fe concentration. However, the substitution of Zn by Fe results in five additional bands with frequencies between the TO (271 cm⁻¹) and LO (350 cm⁻¹) modes. Three of these bands are attributed to resonance modes (i.e. Y ₁, Y ₂ and Y ₃ modes). The fourth band (B mode) is assigned to a breathing mode of the nearest-neighbor sulfur atoms around the Fe atoms. The band at 337 cm⁻¹ is attributed to the presence of Fe³⁺. The excellent correlations between the normalized intensities of these five different modes and x _Fe show that these modes depend on Fe-content. Another extra mode at 287 cm⁻¹ is assigned to the presence of Cd in sphalerite.     

Raman spectroscopic features of Al- Fe3+- poor magnesiochromite and Fe2+- Fe3+- rich ferrian chromite solid solutions

Mineralogy and Petrology - Naturally occurring Al- Fe3 +- poor magnesiochromite and Fe2+- Fe3 +- rich ferrian chromite solid solutions have been analyzed by micro-Raman spectroscopy....     

Full operator algorithm for hybrid simulation

One of the weaknesses of the operator splitting method (OSM) is that its corrector step employs the approximation that incremental forces are linearly related to the tested structure's initial stiffness matrix. This paper presents a new predictor–corrector technique in which the assumptions about the tested structure's response are shifted to the predictor step, which results in an enhancement in overall simulation accuracy, especially for nonlinear structures. Unlike OSM, which splits the displacement and velocity operators into explicit and implicit terms, the new method uses predicted accelerations to compute fully explicit displacement and velocity values in the predictor step. Another advantage of the proposed technique, termed the full operator method (FOM) is that its formulation makes it suitable for both quasi‐static and real‐time hybrid simulation. The effectiveness of FOM is first evaluated by investigating error propagation in an undamped single degree‐of‐freedom model. It is shown that the corrector step in FOM is able to significantly suppress aberrant simulation results caused by incorrect estimation of the structure's stiffness matrix. The performance of FOM is demonstrated by exercising two additional models, which exhibit significant inelastic behavior under the prescribed excitation. The simulation results show that the proposed FOM algorithm is capable of producing accurate solutions and that the corrector step is influential in effectively reducing simulation errors. It is also shown that FOM suppresses actuator displacement control errors because of its reliance on measured quantities in the corrector step. Copyright © 2009 John Wiley & Sons, Ltd.     

Coastal vulnerability to sea-level rise: a spatial–temporal assessment framework

The scientific community is confident that warming of the Earth’s climate is unequivocal. Sea-level rise, which poses potential threats to coastal areas, is one of the most recognised possible impacts of this climate change. The nonlinearities, complexities, and spatial and temporal lags are common characteristics of coastal processes driven by human and natural interaction. With the acknowledgement of the complexity and dynamic nature of coastal systems, this paper introduces a spatial–temporal assessment framework, for addressing both the temporal and spatial variations, when assessing the vulnerability of natural and human systems in coastal areas. The framework is based upon a combination of system dynamics (SD) modelling and geographical information systems by taking into account spatial (x, y, z) and temporal (t) dimensions. The strategy of the adopted approach is to use the loose coupling approach by which a spatial model component is incorporated into a SD model component through a data converter.     

Natural radioactivity in basement rocks and stream sediments, Sharm El Sheikh Area, South Sinai, Egypt: radiometric levels and their significant contributions

The present study examines the natural radioactivity in basements rocks including granites and associated dikes besides stream sediments in Sharm El Sheikh area. Two main rock units are concerned; granites pertaining to Younger Granites of Precambrian age and clastic sedimentary rocks related to Miocene and Pliocene ages. This area is traversed by two shear zones that were delineated as the master fractures trending NW and NNE and controlling uranium and thorium enrichment in granites and dikes. The field and laboratory radiometric measurements revealed radiometric anomalies, in particular, along shear zones. The results of radiometric analyses including concentrations of equivalent uranium (eU), equivalent thorium (eTh), Ra, and K radionuclides as well as the calculated ratios eTh/eU and eU/Ra for representative samples belonging to all rock varieties, revealed that the felsic dikes have the highest values of the average radionuclides potential followed by the alkali feldspar granites, while the mafic dikes display the lowest radioactivity potential. On the other hand, the trends defined in the variation of uranium and thorium reflects the amount of remobilization of uranium that has occurred within the plutons. The eTh and eU/eTh ratios shows a negative correlation, suggesting that distribution of uranium and thorium was at least controlled by magmatic differentiation, while, the positive correlation between eU and eU/eTh ratios indicates enrichment of uranium through post magmatic processes. Some precautions and recommendations are proposed to avoid any possible environmental impacts from shear zone areas with high intensity of natural radiation sources.     

Imaging soil moisture using GPR tomography and reflection field experiments

We performed GPR tomography and GPR reflection field experiments using a 500-MHz antenna to image relative soil moisture distribution around a poplar tree at the botanic garden of Kiel University, Kiel, Germany. The GPR tomography field experiment is carried out in two consecutive phases in order to obtain ray paths traveling from all directions and intensively covering the target. The radar tomographic data are inverted using the authors’ developed software code SeismoRad based on the finite difference technique. The attained Root-Mean-Square (RMS) errors after 200 iterations between the measured and calculated times range between 1.066 and 5.7 % in the two tomography experiments. The estimated GPR velocities range between 5.3 and 15.1 cm/ns. Two low-GPR velocity zones could be delineated coinciding with the locations of the tree root zone and a previously excavated sector. The high water saturation zone around the tree root system is found to be the main reason for such a decrease in GPR velocity. Interpretation of the two phases proved that the coverage of ray paths from all directions is important to delineate the effect of the poplar tree root system and hence to obtain accurate tomographic results. Furthermore, four GPR reflection lines are performed along the sides of the four trenches such that the antenna is moved longitudinally in the trenches and the radargrams are recorded along the horizontal xy-plane parallel to the ground surface. On the processed GPR reflection radargrams, relatively high-amplitude GPR anomalies could be outlined and are attributed to the boundary between the saturated and wet zones where different water contents affect the GPR velocity. Comparable results are obtained between the tomogram and the radar reflection results with respect to zones of increase in water content.     

Errors of kinematic wave and diffusion wave approximations for time‐independent flows with infiltration and momentum exchange included

Error equations for kinematic wave and diffusion wave approximations were derived for time‐independent flows on infiltrating planes and channels under one upstream boundary and two downstream boundary conditions: zero flow at the upstream boundary, and critical flow depth and zero depth gradient at the downstream boundary. These equations specify error in the flow hydrograph as a function of space. The diffusion wave approximation was found to be in excellent agreement with the dynamic wave approximation, with errors below 2% for values of KF (e.g. KF ≥ 7·5), where K is the kinematic wave number and F is the Froude number. Even for small values of KF (e.g. KF = 2·5), the errors were typically less than 3%. The accuracy of the diffusive approximation was greatly influenced by the downstream boundary condition. For critical flow depth downstream boundary condition, the error of the kinematic wave approximation was found to be less than 10% for KF ≥ 7·5 and greater than 20% for smaller values of KF. This error increased with strong downstream boundary control. The analytical solution of the diffusion wave approximation is adequate only for small values of K. Copyright © 2005 John Wiley & Sons, Ltd.     

Study the feasibility of using PPP for establishing CORS network

Nowadays many continuously operating reference stations (CORS) network were established in Middle East to improve the surveying tasks. Establishing such geodetic control networks can be a costly business where multiple stations should be occupied simultaneously and post-processed with scientific software. Recently, precise point positioning (PPP) provides precise positioning values that may be an alternative to precise relative processing. The current research aims to investigate that PPP has a potential as a reliable absolute positioning technique operational simplicity as well as to investigate the capability of PPP approach to be a low cost alternative to the conventional positioning methods used in position determination of core networks stations. In comparison with common relative GPS techniques, the costs are reduced; because no base stations and no simultaneous observations are necessary, no need for control network maintenance which could be the most defective factors that Egypt HARN network suffered from. To see the feasibility study of using PPP for precise determination of the CORS, 14 days of GNSS data for the 14 Kuwait integrated with 27 IGS stations were processed by Bernese software to calculate the precise coordinates of Kuwaiti CORS network in the latest terrestrial geodetic frame. Three days of these data were processed by Trimble business center software and using PPP approach to calculate the precise coordinates of Kuwait network. In the current research, a comparable investigation was carried out between the coordinates obtained from Bernese software, Trimble business center, and PPP approach. The comparison proved high level of agreement between the coordinates which confirm that PPP approach can be applied for establishment of CORS network.     

A method for estimating specimen tangent stiffness for hybrid simulation

Researchers have long recognized the importance and potential benefits of utilizing the tangent stiffness matrix of a test specimen in hybrid simulations employing implicit and mixed‐integration schemes. However, the computation of the tangent stiffness matrix during testing has proved to be challenging, particularly for test specimens with more than one degree of freedom (dof). This paper presents a new methodology that is more straightforward and simpler than existing techniques for computing the tangent stiffness matrix of a multi‐dof test specimen. The proposed method is combined with the operator‐splitting method (OSM), and the capabilities, advantages and limitations of the new formulation are demonstrated through several examples. The accuracy, stability, and error propagation characteristics of the modified OSM are also studied theoretically as well as numerically. The research results show that the proposed algorithm provides results that are better than those produced via the regular OSM alone, especially for damped structures undergoing highly inelastic behavior during testing. Copyright © 2008 John Wiley & Sons, Ltd.