• Volume 117, Issue 2

      April 2008,   pages  103-178

    • Finite element modelling of elastic intraplate stresses due to heterogeneities in crustal density and mechanical properties for the Jabalpur earthquake region, central India

      A Manglik S Thiagarajan A V Mikhailova Yu Rebetsky

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      Deep lower crustal intraplate earthquakes are infrequent and the mechanism of their occurrence is not well understood. The Narmada–Son-lineament region in central India has experienced two such events, the 1938 Satpura earthquake and the 1997 Jabalpur earthquake, having a focal depth of more than 35 km. We have estimated elastic stresses due to the crustal density and mechanical properties heterogeneities along the Hirapur–Mandla profile passing through the Jabalpur earthquake region to analyse conditions suitable for the concentration of shear stresses in the hypocentral region of this earthquake. Elastic stresses have been computed by a finite element method for a range of material parameters. The results indicate that the shear stresses generated by the density heterogeneities alone are not able to locally enhance the stress concentration in the hypocentral region. The role of mechanical properties of various crustal layers is important in achieving this localization of stresses. Among a range of material parameters analysed, the model with a mechanically strong lower crust overlying a relatively weak sub-Moho layer is able to enhance the stress concentration in the hypocentral region, implying a weaker mantle in comparison to the lower crust for this region of central India.

    • Relationship between chemical composition and magnetic susceptibility in sediment cores from Central Indian Ocean Basin

      J N Pattan G Parthiban V K Banakar A Tomer M Kulkarni

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      Three sediment cores in a north–south transect (3°N to 13°S) from different sediment types of the Central Indian Ocean Basin (CIOB) are studied to understand the possible relationship between magnetic susceptibility (𝜒) and Al, Fe, Ti and Mn concentrations. The calcareous ooze core exhibit lowest 𝜒 (12.32 × 10-7m3 kg−1), Al (2.84%), Fe (1.63%) and Ti (0.14%), terrigenous clay core with moderate 𝜒 (29.9 × 10-7 m3 kg−1) but highest Al (6.84%), Fe (5.20%) and Ti (0.44%), and siliceous ooze core with highest 𝜒 (38.06 × 10-7 m3 kg−1) but moderate Al (4.49%), Fe (2.80%) and Ti (0.19%) contents. The distribution of 𝜒 and detrital proxy elements (Al, Fe, and Ti) are identical in both calcareous and siliceous ooze. Interestingly, in terrigenous core, the behaviour of 𝜒 is identical to only Ti content but not with Al and Fe suggesting possibility of Al and Fe having a non-detrital source.

      The occurrence of phillipsite in terrigenous clay is evident by the Al-K scatter plot where trend line intersects K axis at more than 50% of total K suggesting excess K in the form of phillipsite. Therefore, the presence of phillipsite might be responsible for negative correlation between 𝜒 and Al (𝑟 = −0.52). In siliceous ooze the strong positive correlations among 𝜒, Alexc and Feexc suggest the presence of authigenic Fe-rich smectite. High Mn content (0.5%) probably in the form of manganese micronodules is also contributing to 𝜒 in both calcareous and siliceous ooze but not in the terrigenous core where mean Mn content (0.1%) is similar to crustal abundance. Thus, 𝜒 systematically records the terrigenous variation in both the biogenic sediments but in terrigenous clay it indirectly suggests the presence of authigenic minerals.

    • Evaluation of coal bed methane potential of coal seams of Sawang Colliery, Jharkhand, India

      Anil M Pophare Vinod A Mendhe A Varade

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      The coal seams of Sawang Colliery, East Bokaro Coalfields are bituminous to sub-bituminous in nature and categorized as high gaseous seams (degree II to degree III level). These seams have the potential for coal bed methane (CBM) and their maturity increases with increasing depth, as a result of enhanced pressure-temperature conditions in the underground. The vitrinite maceral group composition of the investigated coal seams ranges from 62.50-83.15%, whereas the inertinite content varies from 14.93-36.81%. The liptinite content varies from 0.66% to 3.09%. The maximum micro-pores are confined within the vitrinite group of macerals. The coal seams exhibit vitrinite reflectance values (Ro% calculated) from 0.94% (sample CG-97) to 1.21% (sample CG-119).

      Proximate analyses of the investigated coal samples reveal that the moisture content (M%) ranges from 1.28% to 2.98%, whereas, volatile matter (VM%) content is placed in the range of 27.01% to 33.86%. The ash content (A%) ranges from 10.92% to 30.01%. Fixed carbon (FC%) content varies from 41.53% to 55.93%. Fuel ratio variation shows a restricted range from 1.53 to 1.97. All the coal samples were found to be strongly caking and forming coke buttons.

      The present study is based on the adsorption isotherm experiments carried out under controlled P-T conditions for determination of actual gas adsorption capacity of the coal seams. This analysis shows that the maximum methane gas adsorbed in the coal sample CG-81 is 17m3/t (Std. daf), at maximum pressure of 5.92MPa and experimental temperature of 30°C. The calculated Langmuir regression parameters $P_L$ and $V_L$ range from 2.49 to 3.75MPa and 22.94 to 26.88m3/t (Std. daf), respectively.

    • Integrated approach for identification of potential groundwater zones in Seethanagaram Mandal of Vizianagaram District, Andhra Pradesh, India

      N C Mondal S N Das V S Singh

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      Identifying a good site for groundwater exploration in hard rock terrain is a challenging task. In hard rocks, groundwater occurs in secondary porosity developed due to weathering, fracturing, faulting, etc., which is highly variable within short distance and contributing to near-surface inhomogeneity. In such situations topographic, hydrogeological and geomorphological features provide useful clues for the selection of suitable sites.

      Initially, based on satellite imagery, topographical, geomorphological and hydrogeological features, an area of about 149km2 was demarcated as a promising zone for groundwater exploration in the hard rock tract of Seethanagaram Mandal, Vizianagaram District, Andhra Pradesh, India. A total of 50 Vertical Electrical Soundings (VES) were carried out using Wenner electrode configuration. An interactive interpretation of the VES data sharpened the information inferred from geomorphological and hydrogeological reconnaissance. Ten sites were recommended for drilling. Drilling with Down-The-Hole Hammer (DTH) was carried out at the recommended sites down to 50 to 70m depths. The interpreted VES results matched well with the drilled bore well lithologs. The yields of bore wells vary from 900 to 9000 liters per hour (lph).

    • An application of artificial intelligence for rainfall–runoff modeling

      Ali Aytek M Asce Murat Alp

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      This study proposes an application of two techniques of artificial intelligence (AI) for rainfall–runoff modeling: the artificial neural networks (ANN) and the evolutionary computation (EC). Two different ANN techniques, the feed forward back propagation (FFBP) and generalized regression neural network (GRNN) methods are compared with one EC method, Gene Expression Programming (GEP) which is a new evolutionary algorithm that evolves computer programs. The daily hydrometeorological data of three rainfall stations and one streamflow station for Juniata River Basin in Pennsylvania state of USA are taken into consideration in the model development. Statistical parameters such as average, standard deviation, coefficient of variation, skewness, minimum and maximum values, as well as criteria such as mean square error (MSE) and determination coefficient $(R^2)$ are used to measure the performance of the models. The results indicate that the proposed genetic programming (GP) formulation performs quite well compared to results obtained by ANNs and is quite practical for use. It is concluded from the results that GEP can be proposed as an alternative to ANN models.

    • A Statistical Cyclone Intensity Prediction (SCIP) model for the Bay of Bengal

      S D Kotal S K Roy Bhowmik P K Kundu Ananda Kumar Das

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      A statistical model for predicting the intensity of tropical cyclones in the Bay of Bengal has been proposed. The model is developed applying multiple linear regression technique. The model parameters are determined from the database of 62 cyclones that developed over the Bay of Bengal during the period 1981–2000. The parameters selected as predictors are: initial storm intensity, intensity changes during past 12 hours, storm motion speed, initial storm latitude position, vertical wind shear averaged along the storm track, vorticity at 850 hPa, Divergence at 200 hPa and sea surface temperature (SST). When the model is tested with the dependent samples of 62 cyclones, the forecast skill of the model for forecasts up to 72 hours is found to be reasonably good. The average absolute errors (AAE) are less than 10 knots for forecasts up to 36 hours and maximum forecast error of order 14 knots occurs at 60 hours and 72 hours. When the model is tested with the independent samples of 15 cyclones (during 2000 to 2007), the AAE is found to be less than 13 knots (ranging from 5.1 to 12.5 knots) for forecast up to 72 hours. The model is found to be superior to the empirical model proposed by Roy Bhowmik et al (2007) for the Bay of Bengal.

    • North Indian Ocean warming and sea level rise in an OGCM

      Bijoy Thompson C Gnanaseelan Anant Parekh P S Salvekar

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      The variability in the long-term temperature and sea level over the north Indian Ocean during the period 1958–2000 has been investigated using an Ocean General Circulation Model, Modular Ocean Model version 4. The model simulated fields are compared with the sea level observations from tide-gauges, Topex/Poseidon (T/P) satellite, in situ temperature profile observations from WHOI moored buoy and sea surface temperature (SST) observations from DS1, DS3 and DS4 moored buoys. It is seen that the long (6–8 years) warming episodes in the SST over the north Indian Ocean are followed by short episodes (2–3 years) of cooling. The model temperature and sea level anomaly over the north Indian Ocean show an increasing trend in the study period. The model thermocline heat content per unit area shows a linear increasing trend (from 1958–2000) at the rate of 0.0018 × 1011J/m2 per year for north Indian Ocean. North Indian Ocean sea level anomaly (thermosteric component) also shows a linear increasing trend of 0.31mm/year during 1958–2000.

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