Application of sequential Gaussian simulation to quantify the surface wave magnitude uncertainty within the faulted regions

Geostatistical simulations have been recently widely used in the geological and mining investigations. Variogram, the fundamental tools of geostatistics, can identify the spatial distribution of the regionalized variable within the area. One of the important issues of geostatistical simulation in seismotectonics is producing uncertainty maps, which could be applicable to predict earthquake parameters through the site locations especially for civil structures like bridges. It can help engineers to design the structure of interest better. Earthquake parameters as for example seismic fault and surface wave magnitude (Ms) have significant impact on the feasibility study of the civil structures. In this research, a method is presented to produce uncertainty maps for seismic fault and surface wave magnitude, Ms. For this aim, information related to surface wave magnitude and fault trace in Zagros region (SW of Iran) has been collected. Then, the relationships between them through the site location have been investigated and analyzed by conditional geostatistical simulation. In order to quantify the uncertainty of each parameter, the uncertainty formula after generating the E-type maps has been provided and discussed. Finally, in “Talgah Bridge” site, these uncertainty maps were produced to interpret the impact of the surface wave magnitude and fault trace in this specific civil structure.     

Water demand management in Yemen and Jordan: addressing power and interests

This paper investigates the extent to which entrenched interests of stakeholder groups both maintain water use practice, and may be confronted. The focus is on the agricultural sectors of Yemen and Jordan, where water resource policymakers face resistance in their attempts to reduce water use to environmentally sustainable levels through implementation of water demand management (WDM) activities. Some farmers in both countries that have invested in irrigated production of high-value crops (such as qat and bananas) benefit from a political economy that encourages increased rather than reduced water consumption. The resultant over-exploitation of water resources affects groups in unequal measures. Stakeholder analysis demonstrates that the more ‘powerful’ groups (chiefly the large landowners and the political elites, as well as the ministries of irrigation over which they exert influence) are generally opposed to reform in water use, while the proponents of WDM (e.g. water resource managers, environmental ministries and NGOs, and the international donor community) are found to have minimal influence over water use policy and decisionmaking. Efforts and ideas attempted by this latter group to challenge the status quo are classified here as either (a) influencing or (b) challenging the power asymmetry, and the merits and limits of both approaches are discussed. The interpretation of evidence suggests current practice is likely to endure, but may be more effectively challenged if a long-term approach is taken with an awareness of opportunities generated by windows of opportunity and the participation of ‘overlap groups’.     

Earthquake Hazard Assessment in the Oran Region (Northwest Algeria)

This paper deals with the probabilistic seismic hazard analysis carried out in the Oran region, situated in the Northwest of Algeria. This part of Algeriawas historically struck by strong earthquakes. It was particularly affected during theOctober 9, 1790 Oran earthquake of intensity X. The main purpose of this work is to assessseismic hazard on rocks in order to provide engineers and planners with a basic tool for seismicrisk mitigation. The probabilistic approach is used in order to take into account uncertaintiesin seismic hazard assessment. Seismic sources are defined in the light of the most recentresults obtained from seismotectonics analyses carried out in North Algeria.Source parameters such as b-values, slip rate and maximum magnitude are assessed for eachseismic source. The attenuation of ground shaking motion with distance is estimated byusing attenuation relationships developed elsewhere throughout the world (Sadigh et al., 1993; Ambraseys and Bommer, 1991). The two relationships agree well with the local data. Differentchoices of source parameter values and attenuation relationships are assigned weights in alogic tree model. Results are presented as relationships between values of peak groundacceleration (PGA) and annual frequency of exceedance, and maps of hazard for returnperiods of 200 years and 500 years. A maximum peak ground acceleration of 0.42 g is obtainedfor the Oran site for a return period of 500 years.     

Foundation settlement statistics via finite element analysis

The dispersion observed in soil data comes both from the spatial variability which greatly influences the behavior of large structures and from errors in testing. Thus, the geotechnical engineering deals with uncertainties for which deterministic approaches are not suitable. The resort to probabilistic techniques, enables modeling uncertainties by analyzing their dispersion effect on the global behavior of the structure. The scope of this paper is analyzing settlement and differential settlement variability of a pair of foundations on random heterogeneous medium. The random soil properties of interest are the elastic modulus, and the Poisson ratio. The elastic modulus is modeled as a spatially random field by adopting the lognormal distribution, which enables analyzing its large variability. Because soil Poisson ratio is bounded in practice between two extreme values, its random field is obtained by using the Beta distribution. In this study, one proposes for the Beta field determination, a mapping technique on the probability distribution function diagram, by solving a non-linear equation. However, the mean and variance are unchanged through the mapping operation. Because the soil Poisson ratio is a positive parameter, one prefers to perform the mapping operation with the probability function of the lognormal distribution. Also, the proposed technique can be used for other bounded soil properties such as the porosity. In this paper, settlement and differential settlement statistics prediction are carried out using Monte Carlo simulations combined with deterministic finite element method (DFEM). A performed parametric study shows the following: (i) as the variability of the elastic modulus increases as settlement and differential settlement statistics are important, also, settlement statistics decreases as the Poisson ratio variability increases, and differential settlement statistics do not seem be affected by its variability. (ii) settlement and differential settlement statistics are important for positive inter-property correlation. (iii) a great influence of the correlation lengths on settlement and differential settlement statistics.     

A three‐phase model for unsaturated soils

A comprehensive framework to define the constitutive behaviour of unsaturated soils is developed within the theory of mixtures applied to three‐phase porous media. Each of the three phases is endowed with its own strain and stress. Elastic and elastic–plastic constitutive equations are developed. Particular emphasis is laid on the interactions between the phases both in the elastic and plastic regimes. Nevertheless, the clear structure of the constitutive equations requires a minimal number of material parameters. Their identification is provided: in particular, it incorporates directly the soil–water characteristic curve. Crucial to the formulation is an appropriate definition of the effective stress. The coupled influence of this effective stress and of suction makes it possible to describe qualitatively many of the characteristic features observed in experiments, e.g. for normally consolidated soils, a plastic behaviour up to air entry followed by an elastic behaviour at increasing suctions, and, on the way back, an elastic behaviour, unless compression is applied in which case plastic collapse occurs. Copyright © 2000 John Wiley & Sons, Ltd.     

Numerical modeling of general circulation,thermohaline structure,and residence time in Gorgan Bay,Iran

Gorgan Bay is a semi-enclosed basin located in the southeast of the Caspian Sea, Iran. The bay is recognized as a resting place for migratory birds as well as a spawning habitat for native fish. However, apparently, no detailed research on its physical processes has previously been conducted. In this study, a 3D coupled hydrodynamic and solute transport model was used to investigate general circulation, thermohaline structure, and residence time in Gorgan Bay. Model outputs were validated against a set of field observations. Bottom friction and attenuation coefficient of light intensity were tuned in order to achieve optimum agreement with the observations. Results revealed that, due to the interaction between bathymetry and prevailing winds, a barotropic double-gyre circulation, dominating the general circulation, existed during all seasons in Gorgan Bay. Furthermore, temperature and salinity fluctuations in the bay were seasonal, due to the seasonal variability of atmospheric fluxes. Results also indicated that under the prevailing winds, the domain-averaged residence time in Gorgan Bay would be approximately 95 days. The rivers discharging into Gorgan Bay are considered as the main sources of nutrients in the bay. Since their mouths are located in the area with a residence time of over 100 days, Gorgan Bay could be at risk of eutrophication; it is necessary to adopt preventive measures against water quality degradation.     

Categorization of Mineral Resources Based on Different Geostatistical Simulation Algorithms: A Case Study from an Iron Ore Deposit

Mineral resource classification plays an important role in the downstream activities of a mining project. Spatial modeling of the grade variability in a deposit directly impacts the evaluation of recovery functions, such as the tonnage, metal quantity and mean grade above cutoffs. The use of geostatistical simulations for this purpose is becoming popular among practitioners because they produce statistical parameters of the sample dataset in cases of global distribution (e.g., histograms) and local distribution (e.g., variograms). Conditional simulations can also be assessed to quantify the uncertainty within the blocks. In this sense, mineral resource classification based on obtained realizations leads to the likely computation of reliable recovery functions, showing the worst and best scenarios. However, applying the proper geostatistical (co)-simulation algorithms is critical in the case of modeling variables with strong cross-correlation structures. In this context, enhanced approaches such as projection pursuit multivariate transforms (PPMTs) are highly desirable. In this paper, the mineral resources in an iron ore deposit are computed and categorized employing the PPMT method, and then, the outputs are compared with conventional (co)-simulation methods for the reproduction of statistical parameters and for the calculation of tonnage at different levels of cutoff grades. The results show that the PPMT outperforms conventional (co)-simulation approaches not only in terms of local and global cross-correlation reproductions between two underlying grades (Fe and Al₂O₃) in this iron deposit but also in terms of mineral resource categories according to the Joint Ore Reserves Committee standard.

     

Surface electrical resistivity tomography and hydrogeological characterization to constrain groundwater flow modeling in an agricultural field site near Ferrara (Italy)

A portion of an unconfined alluvial aquifer located in the Padana Plain (Italy) was characterized following an integrated hydro-geophysical approach. Initially an electrical resistivity tomography (ERT) survey was employed to localize the boundaries of a modest paleo-channel body and to design the installation of a groundwater monitoring network. Multilevel slug-tests were performed to estimate the aquifer’s saturated hydraulic conductivities. Determined permeability values together with electrical resistivity data were correlated. The correlation resulted in a site specific bi-logarithmic linear relationship. Based on this relationship, punctually determined hydraulic conductivities were spatially extended over the studied flow domain. Finally, continuously measured piezometric heads were used to calibrate a 3D flow model. Sensitivity analysis was performed to confirm the reliability of the reconstructed permeability field, as well as, to assess the minimum number of direct measurements needed to safely characterize the selected aquifer portion. The integration of the ERT survey results with the classical hydrogeological tests can be conveniently applied to constrain the permeability field during flow model calibration. Although the applicability of the determined relationship is site specific, the followed procedure is useful especially when there is a need to optimize the available resources and in case of small-scale pilot studies.     

Partitioning of metals in sediments of the Haraz River (Southern Caspian Sea basin)

The Haraz River flows northwards through the Iranian Alborz mountains in the central region of Mazandaran province and empties into the Caspian Sea. This area has been a rich source of minerals from times immemorial. About 45 mines (coal, limestone, sand and gravel, etc.) have been operational for the last eight decades. Towards the estuary, the river receives a discharge of industrial, agricultural and urban wastes. Eight sediment samples from the Haraz River and its main tributaries were collected and analyzed for base metals as well as Sr and Fe. The chemical partitioning of metals (Cu, Zn, As, Cd, Pb, Fe, Ni, Cr, Co and Sr) in each sample was determined in four fractions (acid-soluble, reducible, oxidizable and residual). The total content of each metal was also determined. The results showed relatively higher concentrations of Cd, As, Sr and Pb in comparison to that of shale. However, based on the chemical partitioning of metals, it is found that Pb, Co, Cd and Sr are the most mobile metals. In spite of the high As concentrations in sediments, it is not likely that this element is a major hazard for the aquatic environment, since it is found mainly in the residual fraction. Cadmium is the metal that showed the highest percentages in the acid-soluble fraction (the most labile) and the lowest in the residual fraction. However, Fe, Cr and Ni are present in the greatest percentages in the residual fraction, which implies that these metals are strongly linked to the sediments.