July, 2015

July, 2015   ||  Volume 19 No.3



Thermo-mechanical structure of the Indian continental lithosphere

Ajay Manglik

CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad - 500007, INDIA
*Corresponding Author: ajay@ngri.res.in


Thermo-mechanical properties of the rocks constituting the lithosphere control the nature of lithospheric deformation at multi-scales. The oceanic lithosphere, being simple in terms of the crustal structure, composition, and the thermal structure, in general has a fairly well defined thermo-mechanical structure. Significant variations in the crustal thickness and composition, complex evolutionary history, and variations in the composition and viscosity of the mantle part of the lithosphere due to varying degree of depletion of incompatible elements lead to a very complex mechanical structure of the continental lithosphere. This paper presents a brief review of the modeling studies carried out to estimate the mechanical/ thermo-mechanical properties and structure of the Indian continental lithosphere. A synthesis of the results obtained by various approaches reveals two major inferences and the discrepancies in the estimates of the mechanical strength of the Indian continental lithosphere. First inference is that the Indian shield can be broadly sub-divided into the northern and the southern segments based on the mechanical strength of the lithosphere, with the Central Indian Tectonic Zone forming the contact between the two segments. Second inference is that there are variations in the mechanical strength of the northern Indian shield along the strike of the Himalayan collision belt. The observations of the lowest surface heat flow in the Archaean western Dharwar craton implying the thickest lithosphere in this region and the low effective elastic thickness for the southern shield obtained by the admittance and coherence analyses present an exciting paradoxical scenario having implications for the tectonic deformation of the Indian continental lithosphere in response to the plate boundary forces. An integration of the new geophysical images of the Indian continental lithosphere and thermo-mechanical modeling can help in resolving the discrepancy.


Groundwater prospecting in Deccan traps covered Tawarja basin using Electrical Resistivity Tomography

S.N. Rai*1, S.Thiagarajan2, G.B.K. Shankar2, M. Sateesh Kumar2, V. Venkatesam2, G. Mahesh2, and R. Rangarajan2

1Presently at Department of Earth Sciences, IIT Roorkee, Roorkee-246 667, U.K., India
2CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad-500 007, India
*Corresponding Author:snrai_ngri@yahoo.co.in

Acute shortage of water supply for domestic and irrigation purposes in hard rock area is accentuated by occurrence of groundwater in limited quantity within sparsely distributed aquifers characterised with secondary porosity of finite areal extent. Tawarja river basin is in drought prone Latur district of India falling in basaltic Deccan Volcanic Province (DVP). which occupies half a million square km area. Because of availability of limited quantity of groundwater in the shallower aquifers, ever increasing withdrawal of groundwater in excess to recharge is resulting in continuous declining of water table. As a result bore wells/ dug wells used for groundwater pumping from shallower aquifers often go dry, with the onset of summer season. Locating of groundwater potential zones by bore well drilling, in the absence of scientific investigations, is fraught with high percentage of failure. Therefore, delineation of deeper sources of groundwater with certainty based on scientific investigations is urgently needed to meet the ever increasing demand for water supply. This paper presents results of 2-D Electrical Resistivity Tomography carried out in part of Tawarja basin, a complex geo-environ, to demonstrate its efficacy in delineation of groundwater potential zones and sites of aquifer recharging. Several sites suitable for bore well drilling have been identified, which can be developed to meet the water supply demand in the investigated region.


Geological and Geotechnical Characterisation Using Geophysical Logs – An Example from Adriyala Longwall Project of Singareni Collieries, Telangana, India
M. Shanmukha Rao1 and G. Uday Bhaskar*2
1Superintending Geophysicist, Exploration Division, SCCL, Kothagudem, ms_rao_gp@yahoo.com
2 DGM (Geophysics), Exploration Division, SCCL, Kothagudem, uday_bhaskar_g@yahoo.com
*Corresponding Author: uday_bhaskar_g@yahoo.com

The studies conducted at Adriyala longwall block of Singareni Collieries Company Limited (SCCL) in the state of Telangana, India conclude that geophysical logs comprising electrical, density, neutron, caliper, Full Waveform Sonic (FWS) and acoustic image probes can provide reliable geological and geotechnical models required for longwall mining. The basic lithological details, sedimentary features and associated geotechnical risks are interpreted using these logs. The P wave velocities obtained from sonic logs are correlated with the lab determined strength parameters such as uniaxial compressive strength (UCS), Tensile Strength (TS) and Young’s Modulus. The empirical equations provided a means to construct UCS map of interburden strata of coal seams from sonic data which optimised depending on available core data. The Geophysical Strata Rating (GSR) similar to Coal Mines Roof Rating (CMRR) and Rock Mass Rating (RMR) has also been applied to assess the competency of interburden strata right at the exploration stage itself. The insitu stress directions and master cleats orientation are determined from the acoustic image logs. UCS and GSR maps prepared from geological and geophysical inputs provided an effective means to analyse the competency of immediate overburden of 23m to 28m (SS-80) of Seam-I, which is considered for longwall mining.  
Seam-I was deposited in stable conditions resulting in uniform thickness of 6m of coal including that of 0.40m thick dirt band in the middle. Weak bed in the middle of Seam-I and intertonguing of clay of 1.20m thickness with sandstone along the immediate roof influence working sections and roof support system. Sandstones comprising the overburden strata of coal are very thick massive beds whose UCS and GSR ranges of 6MPa to 8MPa and 30% to 45% classify them as low strength and fair rocks respectively. These massive beds also contain thin to thick beds of good (45% to 60% GSR) and very good (60% to 80% GSR) rocks along with poor rocks having GSR of 15% to 30% at places. Very thick massive beds can create conditions of heavy periodic weighting during longwall extraction while the thin beds contained by it can act as separation planes and reduce the effective thickness of sandstone that could otherwise contribute to periodic weighting.  GSR provides both petrophysical and geotechnical models where as the UCS maps provide details of intact strength only.

Establishing hydrogeophysical relationship between geoelectric and hydraulic parameters for a basaltic aquifer, Ahmednagar district, Maharashtra, India
C. Krishnaiah
Central Water and Power Research Station, Khadakwasla, Pune 411 024, India
E mail: krishnaiahc@yahoo.com

Quantitative assessment of the spatial distribution of intensity of groundwater pollution caused by untreated industrial effluents requires development of numerical transport models which in turn needs information on the spatial distribution of hydraulic characteristics of the subsurface. The most effective way to evaluate such aquifer characteristics is by performing the pump-out tests. However, sparse location of boreholes posed problems in modeling the subsurface pollution at Mula sugar factory area, Ahmednagar district, Maharashtra, India. A well established site specific relationship between geoelectric and hydrogeological parameters of the aquifer was adopted as an alternative approach to assess the hydraulic characteristics of the subsurface layers.
The geoelectrical parameters were determined from the Vertical Electrical Soundings (VES) data carried out at pump-out test wells. The values of hydraulic conductivity (K) and transmissivity (T) computed from the pump-out tests were correlated with the normalized aquifer resistivity (ρ’) and normalized transverse resistance (Z’) respectively which suggested a linear relationship.
This study has established a valuable site specific relationship between hydraulic and electrical parameters in a basaltic aquifer of Mula sugar factory area. The calibrated relationship could contribute to assess the spatial distribution of hydraulic conductivity value as an input to construct a pragmatic numerical model. Hence, the use of geoelectrical soundings provides a cost effective alternative technique for calculating the hydraulic parameters and characterizing the aquifer system of the virgin areas.

A quasi-numerical solution for 3-D meso-scale lee wave associated with meso-scale baroclinic dry mean flow across the Assam-Burma hills in India
Prasanta Das*1, Somenath Dutta2 and Shyamal Kumar Mondal3
1 Department of Mathematics, Ramananda College, Bishnupur, Bankura-722122,W.B., India.
2 India Meteorological Department(IMD), Pune-411008, India.
3 Department of Applied Mathematics with Oceanology and Computer Programming,
Vidyasagar University, Midnapore -721102,W.B., India.
*Corresponding Author : pdas.math1986@gmail.com

In this study an attempt has been made to obtain a 3-D meso-scale lee wave solution associated with a meso-scale flow across the Assam-Burma hills (ABH), following a quasi-numerical approach. To obtain the solution a laminar, Bousisnesq, non-rotational 3-D mean flow with realistic vertical variation of wind and temperature across the ABH have been considered, where both buoyancy frequency(N) and basic flow(U) in the wind are realistically variant with height. ABH has been approximated by two 3-D elliptical barriers, separated by a valley of some finite width and is broadly north-south (NS) oriented. For more simplicity, the basic flow has been assumed to have only one component normal to the major ridges of the barriers. Two cases have been discussed. In every case, we have computed perturbation vertical velocities (w') (wave part) in the central plane at different heights, at different downstream locations. Vertical variation of w'at different downstream locations shows cellular structure. It is also found that the maximum updraft regions associated with lee waves are approximately ‘horseshoe shaped’, concave to down wind direction and spread laterally with vertical.

Assessment of Hydroclimatic Condition in Extensive Groundwater Mining Area, Southern India
Anbazhagan S* and Jothibasu A
Centre for Geoinformatics and Planetary Studies, Department of Geology,
Periyar University, Salem – 636 011, India.
*Corresponding Author :anbu02@gmail.com

The study highlights the climatic water balance, drought assessment and agricultural potentiality of Uppar Odai sub-basin located in the Southern part of India, Tamil Nadu state. The average annual precipitation in the sub-basin is 625 mm, which is much lower than the state average rainfall (970 mm). It has been observed that the intensive agricultural practices and extensive groundwater mining lead to the groundwater decline in the sub-basin. Rainfall data were collected from 1971-2011 for five rain gauge stations. The hydroclimatic potentialities such as precipitation, temperature and water holding capacity are the three primary parameters considered to derive water balance parameters. The secondary water balance components, namely potential evapotranspiration (PET), actual evapotranspiration (AET), water deficit (WD) and water surplus (WS) were derived from these primary parameters. The PET and AET were calculated using Thornthwait’s (1948) and Thornthwaite and Mather (1955) methods respectively. Four water balance indices, namely index of aridity (Ia), index of humidity (Ih), index of moisture (Im) and index of moisture adequacy (Ima) were calculated from secondary water balance components. From the derived indices, drought condition, climatic shift and agricultural potentiality were assessed. The results have indicated that drought condition prevails during every alternate year in the sub-basin.

Assessment of Snowmelt Runoff in the Eastern Himalayan Region under Climate Change Scenarios
A. Bandyopadhyay, A. Bhadra, N. Chiphang*, K.T. Senzeba
Department of Agricultural Engineering, North Eastern Regional Institute of Science and Technology, Nirjuli (Itanagar), Arunachal Pradesh 791109, India.
*Corresponding Author : ecks.wove@gmail.com

In Eastern Himalayan region, snow melt is the major source of fresh water. Also, snow covered areas lying at low altitudes are expected to be most vulnerable to global warming. Thus, assessment of the snowmelt runoff under different climatic scenarios is important for efficient management and planning of water resources, which can be used towards mitigating the influence of climate change. Eastern Himalayan region of India with its unique topography and inaccessibility is lagging behind in the studies related to snow and glacier melt modelling and impact of climate change to water resources. Nuranang river catchment of Tawang River basin located in Tawang district of Arunachal Pradesh was selected as the study area for the present study. Average snow accumulation and depletion patterns of the basin showed a smaller peak in terms of snow cover area percentage (SCA%) in the month of November and a larger one in April. A Windows-based semi-distributed deterministic model was used in this study to predict the snowmelt runoff using degree-day approach , which requires SCA% for different elevation zones as input. The model was calibrated for depletion periods of 2006, 2007, and 2009 and validated for year 2004 satisfactorily. Further, the projected temperature and precipitation data downloaded from NCAR's GIS data portal for different emission scenarios (SRES), viz., A1B, A2, B1; and IPCC commitment (non-SRES) scenario for different future years (2020, 2030, 2040 and 2050) were used to generate snow depletion curves for future and compared with conventional depletion curve for present climatic condition. The same were used to evaluate the future stream flow under different projected climatic scenarios. Evaluation of the impact of climate change showed that change in cumulative snowmelt depth and snow depletion for different future years is highest under A1B and lowest under IPCC Commitment scenarios, whereas A2 and B1 values are in-between A1B and IPCC Commitment.

Quantification of Panchayat-Level Flood Risks in the Bhograi Coastal Block, Odisha, India
Nilay Kanti Barman1, Soumendu Chatterjee2, and *Ansar Khan3
1Department of Geography, Hijli College,Kharagpur-721306, India,nilay@csws.in
2Department of Geography, Presidency University, Kolkata-700073, India, scgeovu@yahoo.co.in
3Department of Geography and Environment Management, Vidyasagar University, Midnapore-721102, India
*Corresponding Author: khanansargeo@gmail.com

This paper assesses coastal flood risks through quantification of flood intensity and impacts across the different local Gram Panchayats (GPs) in the Bhograi block, Odisha, India. With respect to the June 2008 flood event in the region, the enormity of flooding was calculated for each GP using normalized values of measurable parameters relating to flood characteristics. Thus, a Flood Magnitude Rank (FMR) was assigned to each of the GPs according to the degree of flooding intensity. Similarly a Flood Impact Rank (FIR) for each GP was derived from a damage database. The product of the FMR and FIR was used to calculate the Flood Severity Score (FSS) for the concerned GPs, which was then multiplied by the probability of flood event occurrences to obtain a Flood Hazard Score (FHS). This analysis was used to divide the study area into five Flood Hazard Risk zones including (a) very low risk (FHS <1.33); (b) low risk (FHS 1.33–2.07); (c) moderate risk (FHS 2.07–3.02); (d) high risk (FHS 3.02–4.90); and (e) very high risk (FHS >4.90) areas. Narayanmohantiparia, Rasalpur and Kharidpimpal fell into the very high flood hazard risk class, whereas Dehunda, Baunsadiha and Balim tended to be at very low risk from flood hazards. The other 26 GPs in the study area were categorized into low- moderate or high risk zones according to their FHS. Overall, this type of flood hazard risk assessment may prove useful for future environmental planning and management programs in coastal regions.

Design of Gravity energy filter to enhance signal-to-noise ratio of gravity measurements
Shib Sankar Ganguli*,1, 2, Aref A. Lashin3, 4, Nassir S. Al Arifi5 and V.P. Dimri1
1 CSIR-National Geophysical Research Institute (NGRI), Hyderabad - 500 007, India.
2 Academy of Scientific and Innovative Research (AcSIR), CSIR-NGRI, Hyderabad - 500 007, India.
ganguli.ism@gmail.com, vpdimri@gmail.com
3 King Saud University, College of Engineering, Petroleum and Gas Engineering Dept., PO Box 800, Riyadh 11421, Saudi Arabia.
4Benha University, Faculty of Science - Geology Department, P.O. Box 13518, Benha - EGYPT.
5 Geology and Geophysics Department, King Saud University, Riyadh, Saudi Arabia. nalarifi@ksu.edu.sa
*Corresponding Author: ganguli.ism@gmail.com

One of the significant objectives of geophysical data recording and processing is the enhancement of the signal-to-noise ratio, and in this perspective, the design of an optimum digital filter is pivotal. The well-known Wiener-Hopf filter has been successfully applied to attain this objective. In comparison, the output energy filter is a tool, by which one can attempt to enhance the signal-to-noise ratio by retrieving the signal at the output, producing a longer burst of energy in the time interval where the signal occurs. In the present work, we report the development of a digital filter, namely, gravity energy filter for the improvement of gravity signal-to-noise ratio, immersed in coloured noise. For the design of such filter, it is not obligatory to have explicit knowledge of the gravity signal shape; nevertheless, its performance level is not compromised. We demonstrated its applicability on synthetic data, generated by considering two spherical bodies at the subsurface, where in the gravity signal buried in coloured noise beyond visual recognition, is easily detected after filtering.

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