Micro-CT and FIB–SEM imaging and pore structure characterization of dolomite rock at multiple scales

With improvements of imaging techniques and computational power, Digital Rock Physics (DRP) has been increasingly used to determine transport and elastic properties of reservoir core plugs. Since numerical computations highly rely on accurate 3D representations of the porous microstructure of the rocks, the imaging technique and the scale at which the imaging is performed is a critical parameter. In this paper, we introduce a multiscale imaging workflow that uses both micro-X-ray tomography (micro-XCT) and focused ion beam combined with scanning electron microscope (FIB–SEM) to characterize a dolomite rock from the microscale to the nanoscale. This allows for the accurate capture of the different heterogeneities that exist in the carbonate (texture, mineralogy, pore size). The reconstructed microporous structures were then used to successfully predict elastic and permeability properties of selected carbonate.     

Surface water quality contamination source apportionment and physicochemical characterization at the upper section of the Jakara Basin, Nigeria

The present study investigates the surface water quality of three important tributaries of Jakara Basin, northwestern Nigeria to provide an overview of the relationship and sources of physicochemical and biological parameters. A total of 405 water samples were collected from 27 sampling points and analyzed for 13 parameters: dissolved oxygen (DO), 5-day biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), suspended solids (SS), pH, ammonia-nitrogen (NH₃NL), dissolved solids (DS), total solids (TS), nitrates (NO₃), chloride (Cl), phosphates (PO₄), Escherichia coli (E. coli) and fecal coliform bacteria (FCB). Pearson’s product–moment correlation matrix and principal component analysis (PCA) were used to distinguish the main pollution sources in the basin. Four varimax components were extracted from PCA, which explained 84.86, 83.60, and 78.69 % of the variation in the surface water quality for Jakara, Tsakama, and Gama-Kwari Rivers, respectively. Strong positive loading included BOD₅, COD, NH₃NL, E. coli, and FCB with negative loading on DO attribute to a domestic waste water pollution source. One-way ANOVA revealed that there was no significant difference in the mean of the three water bodies (p?>?0.05). It is therefore recommended that the government should be more effective in controlling the point source of pollution in the area.     

Observations of sea ice interannual variations and spring bloom occurrences at the Japanese scallop farming area in the Okhotsk Sea using satellite imageries

The dynamics of ice formation and phytoplankton bloom development in the coastal region of the Okhotsk Sea, Hokkaido, where the Japanese scallop, Mizuhopecten yessoensis, are cultured were investigated using seven years (1998–2004) satellite data from the Special Sensor Microwave/Imager (SSM/I) and Sea-viewing Wide Field-of-view Sensor (SeaWiFS). The interannual variability of sea ice cover and timing of spring bloom occurrences were analyzed. Longer ice cover in 1999, 2001 and 2003 with the presence of ice until early April and shortened ice cover in 1998, 2000, 2002 and 2004 with the occurrence of ice until early March were recognized at this area. Variability in the timing of sea ice retreat and development of spring blooms at the scallop areas were observed. Progression of a single ice edge bloom showed higher Chl-a concentration compared to development of an initial ice edge bloom followed by a later open water bloom. Higher concentration of phytoplankton biomass was observed in the initial bloom when sea ice melting is delayed compared to when the sea ice leaves earlier. Wind events were also observed to affect the occurrences of spring bloom.     

Report on the Diatoms and Dinoflagellates Distribution along the Algerian Coasts: Inter-Region Comparison

The phytoplankton group’s composition is an excellent indicator of the state of coastal waters. The aim of this study is to explore spatial variability of phytoplankton in shallow coastal areas from different regions (East, Center and West) of the Algerian coast. The quantitative and qualitative study of the phytoplankton population was conducted on samples taken during the 2012-2013 period by the research vessel GRINE BELKACEM. The qualitative results show a significant diversity of diatoms and dinoflagellates, which rank first and second in the total flora (Fr > 50%). This finding is also confirmed quantitatively by the abundance values in both 2013 and 2012 samples which largely exceeds the average value in most other areas of the western region (56%) and slightly exceeding 52% in all central areas which represent an equi-distribution between diatoms and dinoflagellates. The Dinoflagellates contribute significantly to the quantitative richness in the eastern region (>60%). The minimum value of Dia/Dino index, recorded in the eastern region confirms the dominance of the dinoflagellates especially in Skikda (0.31) (Skikda).However, our results reveal the presence, in smaller proportion, of other groups such as the cocolithophoridae and euglenophyceae.     

Seismogenic potential and earthquake hazard assessment in the Tell Atlas of Algeria

Seismotectonic zonation studies in the Tell Atlas of Algeria, a branch of the Africa-Eurasia plate boundary, provide a valuable input for deterministic seismic hazard calculations. We delineate a number of seismogenic zones from causal relationships established between geological structures and earthquakes and compile a working seismic catalogue mainly from readily available sources. To this catalogue, for a most rational and best-justified hazard analysis, we add estimates of earthquake size translated from active faulting characteristics. We assess the regional seismic hazard using a deterministic procedure based on the computation of complete synthetic seismograms (up to 1 Hz) by the modal summation technique. As a result, we generate seismic hazard maps of maximum velocity, maximum displacement, and design ground acceleration that blend information from geology, historical seismicity and observational seismology, leading to better estimates of the earthquake hazard throughout northern Algeria. Our analysis and the resulting maps illustrate how different the estimate of seismic hazard is based primarily on combined geologic and seismological data with respect to the one for which only information from earthquake catalogues has been used.     

Substructure design optimization and nonlinear responses control analysis of the mega-sub controlled structural system(MSCSS) under earthquake action

The newly proposed mega sub-controlled structure system(MSCSS) and related studies have drawn the attention of civil engineers for practice in improving the performance and enhancing the structural effectiveness of mega frame structures. However, there is still a need for improvement to its basic structural arrangement. In this project, an advanced, reasonable arrangement of mega sub-controlled structure models, composed of three mega stories with different numbers and arrangements of substructures, are designed to investigate the control performance of the models and obtain the optimal model configuration(model with minimum acceleration and displacement responses) under strong earthquake excitation. In addition, the dynamic parameters that affect the performance effectiveness of the optimal model of MSCSS are studied and discussed. The area of the relative stiffness ratio RD, with different mass ratio MR, within which the acceleration and displacement of the optimal model of MSCSS reaches its optimum(minimum) value is considered as an optimum region. It serves as a useful tool in practical engineering design. The study demonstrates that the proposed MSCSS configuration can efficiently control the displacement and acceleration of high rise buildings. In addition, some analytical guidelines are provided for selecting the control parameters of the structure.     

Surface-rupturing history of the Bree fault scarp, Roer Valley graben: Evidence for six events since the late Pleistocene

Since 1996 paleoseismological investigations have been used to develop the surface- rupturing history of the Bree fault scarp, the morphologically best-defined segment of the southwestern border fault of the Roer Valley graben in northeastern Belgium. The first studies determined that the escarpment is associated with a surface fault, and they exposed evidence for three surface displacements since about 40 ka BP. The most recent eventprobably occurred between 1000 and 1350 yr cal BP. Geophysical and trenching studies at a new site near the southeastern end of the fault scarp reconfirmed the coincidence of the frontal escarpment with a shallow normal fault, which displaces the Middle Pleistocene `Main Terrace' of the Maas River, as well as overlying coversands of Saalian to late Weichselian age. Different amounts of displacement shown by the two youngest coversand units indicate two discrete faulting events, but primary evidence for the coseismic nature of these events is sparse. Radiocarbon and optically stimulated luminescence dating constrainthe age of these events to the Holocene and between 14.0 ± 2.3 ka BP and 15.8 ± 2.9 ka BP, respectively. In addition, four older surface-rupturing events are inferred from the presence of four wedge-shaped units of reworked Main Terrace deposits that are interbedded with coversand units in the hanging wall of the trench and in shallow boreholes. These wedges are interpreted as colluvial wedges, produced by accelerated slope processes in response torejuvenation of the fault scarp, most probably in a periglacial environment. Luminescence dating indicates that five out of a total of six identified faulting events are younger than 136.6 ± 17.6 ka. The antepenultimate event was the largest faulting event, associated with a total fault displacement in excess of 1 m. Thus, the newly investigated trench site represents the longest and most complete record of surface rupturing recovered so far along the Bree fault scarp. This study also demonstrates the viability of the paleoseismological approach to identify past large earthquakes in areas of present-day moderate to low seismic activity.