Magnetic gradient techniques on digitized aeromagnetic data of Ibadan area, south-western Nigeria

Locations and depths to magnetic contacts were estimated from the total intensity magnetic field using the Horizontal Gradient Magnitude (HGM), Analytic Signal Amplitude (ASA) and Local Wavenumber (LWN) methods. Aeromagnetic data from the Ibadan area, in south-western Nigeria, were analyzed to estimate depths to magnetic sources as well as source locations. The minimum/maximum depth limits of the HGM and LWN are relatively close and comparable, while shallow source depths limits are greater than expected in the ASA method when compared with the HGM and LWN functions.     

Mineralogy and equilibrium P-T estimates for peridotite assemblages from the V. Grib kimberlite pipe (Arkhangelsk Kimberlite Province)

This study presents mineralogical and thermobarometric data for equilibrium peridotite assemblages from the V. Grib kimberlite pipe of the Arkhangelsk diamond province. We provided the first constraints on the composition, structure, thermal state, and lower boundary of the lithospheric mantle beneath the V. Grib kimberlite pipe. It was found that phlogopite-free and phlogopite-bearing peridotite xenoliths can be distinguished by their mineral chemistry. The occurrence of phlogopite in peridotites may represent evidence for modal metasomatism responsible for variation in the mineral composition of phlogopite-pyrope and pyrope peridotites. On the basis of P-T estimates, we conclude that modal metasomatism may have affected the entire thickness of the lithospheric mantle beneath the V. Grib kimberlite pipe. Comparison of our results with the available data from the literature shows strong vertical and lateral mantle heterogeneity beneath kimberlite pipes of the Lomonosov deposit and the V. Grib pipe.     

Use of recession-curve analysis for estimation of karstification degree and its application in assessing overflow/underflow conditions in closely spaced karstic springs

In the southern part of the Slovensky Kras Mountains, located on the Hungarian–Slovakian border, a transboundary karstic aquifer Dolny vrch/Alsóhegy underlies the structure and discharges groundwater flow to 15 major karst springs around its margin. Hydrograph recession curves from nine-gauged springs on the Slovak part of the aquifer were analysed, and for each individual spring, depletion hydrograph equations were classified into different categories based on recessional parameters quantitatively describing individual groundwater flow sub–regimes. Discharge depletion was used to create recessional equations, and these were linked to karstification degree, a qualitative scale ranging from 1 to 10. A new application of hydrograph separation was based on examining and combining pairs of springs that likely fit into the category of overflow/underflow springs for a single groundwater reservoir. Recession-curve analysis performed on coupled discharges of two pairs of neighbouring springs was conducted to examine their possible linkage as a single groundwater reservoir, with an overflow outlet and underflow outlet. In the process of discharge coupling, discharges of the springs, hypothesized to be branches of the same source and observed at the same time were simply added together. By analyzing the resulting new time series, a new classification of sub-regimes could be generated. Surprisingly, new facts were revealed about the overflow/underflow springs, which primarily were not recognized previously as being connected components of a single groundwater reservoir. Summations of combined overflow/underflow discharge volumes of a single spring reservoir led to discovery of apparent presence of turbulent flow sub-regimes on the coupled recession curve. Presence of possible overflow/underflow springs of a single groundwater basin should be considered during hydrograph analyses if the springs have attributes that suggest they may be part of a combined flow system. Treating these springs as separate entities as a result can produce significant misinterpretation of drainage parameters. Furthermore, identification of overflow branches facilitates the generation of new research ideas for further speleological investigations nearby, and for assessing the system in a more effective manner.     

Waterlogging and flood hazards vulnerability and risk assessment in Indo Gangetic plain

The recurrent flooding during monsoon and subsequent waterlogging in the northern Bihar plains and the magnitude of losses due to these hazards indicate the continuing vulnerability of the region to flood and waterlogging. Management of floods and waterlogging hazards in highly flood-prone regions of India, including Bihar state has been largely response oriented with little or no attention to mitigation and preparedness. This paper presents a method for spatial, Geographic Information Systems-based assessment of flood and waterlogging vulnerability and risk in northern Bihar plains. Multitemporal satellite data was used to evaluate the area statistics and dynamics of waterlogging over the period from 1975 to 2008. The flood proneness is evaluated at district level with reference to flood inundation during a period from 1998 to 2008. Census data were used to examine the socio-economic characteristics of the region through computation of population density, cultivators, agricultural labourers, sex ratio, children in age group 0–6 years and literates. The geohazard map derived by combining area prone to waterlogging and flood inundation was multiplied with socio-economic vulnerability map to derive the flood-waterlogging risk map of the region. The result shows that flood and water-logging pose highest risk to the central districts in the northern Bihar plains with 50.95% of the total area under high and very high risk.     

Dispersion of love waves in a spherical earth with corrugated surface

Summary Propagation of Love waves over the spherical surface of a layered earth model has been discussed with special emphasis on the dispersion produced in the layer. The velocity of the waves with large wave-length increases appreciably as compared to the case of plane layer. The analysis has been extended to deduce an expression for the dispersion equation of the waves when the upper layer is of varying thickness. The modifications imparted to the dispersion equation depends on the amplitude only and not the shape of the corrugations provided we neglect small quantities of the second order. The effect is a substantial decrease in the phase velocity and becomes more pronounced if the amplitude of the corrugations increases.     

The generation of a pressure profile in a geothermal reservoir: The Mutnovskii hydrothermal steam field

We consider the variation of pressure and temperature along the wellbores in the Mutnovskii hydrothermal steam field. We distinguish three types of barogram to characterize the state of the heat carrier in a well: the subvertical, the subvertical-inclined, and the inclined. The first two types are typical of the wellbore segment filled with the heat carrier in the state of steam and in the two-phase state, and the third is characteristic for the liquid state. A joint analysis of barograms and thermograms gave information on the phase state of the heat carrier along the wellbore and on the conditions peculiar to excitation of a well.     

Analysis of colloidal transfer of strontium-90 with groundwater

The colloidal fractions of various particle sizes were separated from the samples of groundwater in the area of radioactive contamination nearby Obninsk (Kaluga region, Russia). The primary component of the radioactive contamination is ⁹⁰Sr isotope. The colloidal particles were separated from the samples of groundwater by means of ultrafiltration through membranes of 200, 100, and 25 nm pore sizes. The chemical composition of particle surfaces in each of the fractions was determined using X-ray photoelectron spectroscopy. The structure of particles was determined by the changes in the surface composition after the removal of outer layers of particles by etching with argon ions to a depth of 100 Å. It was found that the particles are constituted by inorganic cores mainly of montmorillonite and iron metahydroxide and a broken covering of humic acids. It was shown that about 50% of ⁹⁰Sr is transferred by groundwater with colloidal particles of over 25 nm in size.