Subsurface profiling of granite pluton using microtremor method: southern Aravalli,Gujarat, India

International Journal of Earth Sciences - We report, using the microtremor method, a subsurface granitic pluton underneath the Narukot Dome and in its western extension along a WNW profile, in...     

Assessment of Chock Capacity and Strata Caving for a Longwall Mine

A mine scale numerical analysis of modern day longwall using a 3D Cosserat continuum method has been presented. The effect of mine specific geological conditions on viability of introducing a modern day longwall is comprehensively investigated and analysed in this paper. The various longwall parameters like chock (face support) convergence and strata caving mechanism are evaluated. The varying thickness of the sandstone present in the roof can be seen to have a strong impact on the magnitude and pattern of chock convergence. The paper also discusses the performance of chocks with different capacities under identical conditions. The effect of overlaying sandstone properties and width of the longwall panels have also been investigated. The analyses carried out in this study is expected to provide valuable process guidance during the mine design in relation to selecting the optimal mine geometry and support capacity so that the potential mining hazards could be minimized.     

Structural and luminescent characterisation of uraniferous fluorapatite and haematite associated with phosphatic rocks of the Bijawar group in Sagar District,Madhya Pradesh (India)

The structural and spectroscopic characteristics of phosphatic ferruginous shale samples from the Bijawar Group rocks from Sagar District of Madhya Pradesh (India) have been probed for identification of uranium species. Fluorapatite (\(\hbox {Ca}_{5}\hbox {(PO}_{4})_{3}\hbox {F}\), FAP) and haematite (\(\upalpha \)-\(\hbox {Fe}_{2}\hbox {O}_{3}\)) were identified as the main phases in the separated mineral concentrates. The photoluminescence (PL) and X-ray absorption near edge spectroscopy (XANES) studies pointed to a strong experimental evidence of both U(IV) and U(VI) oxidation states in the mineral concentrate portion obtained from the same parent host rock. The PL spectrum has confirmed the charge transfer (f–d) transition bands in UV and near-UV regions with emission peaks at ca. 290, 313, 336, 399 and 416 nm, which has been attributed to the substitution of \(\hbox {Ca}^{2+}\) ions by U(IV) in FAP and broad structureless emission due to stabilisation of U(VI) as \(\hbox {UO}_{6}^{6-}\) in haematite. Time-resolved spectroscopy studies have revealed biexponential decay components lasting 2–5 ns for U(IV) species and \(10\,\upmu \hbox {s}\) for U(VI) species. These characterisations revealed the fundamental information about the oxidation state and form of uranium in this region. Remediation measures for the Bijawar region are also suggested.     

Active channel systems in the West Basin,Andaman Fore Arc: results from high-resolution bathymetry surveys and GIS analysis

Using multibeam swath bathymetric survey, a moderate sinuosity meandering channel was identified in the West Basin which is extending up to the northwestern corner of the Alcock Rise. Detailed morphometric analysis indicates that this channel is a mature sinuous channel which acts as a major conduit for the sediments into the West Basin. The straight length of the channel is ～70 km with an axial length of ～85 km. Furthermore, the maximum width is 1.5 km and minimum width is 0.4 km with an average sinuosity value of ～1.16, indicating its moderate meandering nature. It is interesting to note that this channel lacks the physical connection with the continental slope of the Andaman and Nicobar Islands. From multibeam data, the channels seem to emerge from Andaman Island; by using GIS techniques, a derived channel network system is obtained to identify the source, which reveals that its exact source is the Irrawaddy Delta system. Furthermore, this study even suggests that the major contribution of modern sediments to the Andaman Fore Arc basin is from Irrawaddy Delta, and sediment supply from Andaman continental slope also played an important role.     

Landslide susceptibility zonation of the Chamoli region, Garhwal Himalayas, using logistic regression model

A remote sensing and Geographic Information System-based study has been carried out for landslide susceptibility zonation in the Chamoli region, part of Garhwal Himalayas. Logistic regression has been applied to correlate the presence of landslides with independent physical factors including slope, aspect, relative relief, land use/cover, lithology, lineament, and drainage density. Coefficients of the categories of each factor have been obtained and used to assess the landslide probability value to ultimately categorize the area into various landslide susceptibility zones; very low, low, moderate, high, and very high. The results show that 71.13% of observed landslides fall in 21.96% of predicted very high and high susceptibility zone, which in fact should be the case. Furthermore, lineament first buffer category (0–500 m) and the east and south aspects are the most influential in causing landslides in the region.     

Variability of Indian monsoonal rainfall over the past 100 ka and its implication for C3–C4 vegetational change

Oxygen and carbon isotope ratios of soil carbonate and carbon isotope ratios of soil organic matter (SOM) separated from three cores, Kalpi, IITK and Firozpur, of the Ganga Plain, India are used to reconstruct past rainfall variations and their effect on ambient vegetation. The δ¹⁸O values of soil carbonate (δ¹⁸O_SC) analyzed from the cores range from ? 8.2 to ? 4.1‰. Using these variations in δ¹⁸O_SC values we are able, for the first time, to show periodic change in rainfall amount between 100 and 18 ka with three peaks of higher monsoon at about 100, 40 and 25 ka. The estimation of rainfall variations using δ¹⁸O value of rainwater-amount effect suggests maximum decrease in rainfall intensity (~ 20%) during the last glacial maximum. The δ¹³C values of soil carbonate (δ¹³C_SC) and SOM (δ¹³C_SOM) range from ? 6.3 to + 1.6‰ and ? 28.9 to ? 19.4‰, respectively, implying varying proportions of C₃ and C₄ vegetations over the Ganga Plain during the last 100 ka. The comparison between monsoonal rainfall and atmospheric CO₂ with vegetation for the time period 84 to 18 ka indicate that relative abundances of C₃ and C₄ vegetations were mainly driven by variations in monsoonal rainfall.     

A direct inversion scheme for deep resistivity sounding data using artificial neural networks

Initialization of model parameters is crucial in the conventional 1D inversion of DC electrical data, since a poor guess may result in undesired parameter estimations. In the present work, we investigate the performance of neural networks in the direct inversion of DC sounding data, without the need ofa priori information. We introduce a two-step network approach where the first network identifies the curve type, followed by the model parameter estimation using the second network. This approach provides the flexibility to accommodate all the characteristic sounding curve types with a wide range of resistivity and thickness. Here we realize a three layer feed-forward neural network with fast back propagation learning algorithms performing well. The basic data sets for training and testing were simulated on the basis of available deep resistivity sounding (DRS) data from the crystalline terrains of south India. The optimum network parameters and performance were decided as a function of the testing error convergence with respect to the network training error. On adequate training, the final weights simulate faithfully to recover resistivity and thickness on new data. The small discrepancies noticed, however, are well within the resolvability of resistivity sounding curve interpretations.     

Trends in seasonal temperatures over the Indian region

An investigation has been carried out to identify the trends in maximum, minimum and mean temperatures and temperature range over the Indian land mass during the winter (January, and February), pre-monsoon (March–May), southwest monsoon (June–September) and post-monsoon (October–December) seasons by using high resolution daily gridded data set prepared by India Meteorological Department for the period of 1969–2005. It has been observed that the maximum temperatures over the west coast of India show rising trend in winter, southwest monsoon and post-monsoon seasons but the maximum temperatures do not show any significant trend over the other parts of the country. Minimum temperatures show increasing trend over the North Indian states in all seasons and they show an increasing trend over the west coast of India in winter and southwest monsoon seasons. Mean temperature shows an increasing trend over the west coast of India during winter and southwest monsoon seasons. Decreasing trend is observed in the temperature range over North India in all seasons due to increasing trend in minimum temperature.