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Volume 14 No.1 January 2010


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Integrated interpretation of seismic, gravity, magnetic and magneto-telluric data in geologically complex thrust belt areas of Manabum, Arunachal Pradesh

G.K.Ghosh, S.K.Basha, M.Salim and V.K.Kulshreshth

1NEF Project, Oil India Limited, Duliajan -786 602
E.mail :gk_ghosh@yahoo.com

Subsurface heterogeneity delineation in the geologically complex and logistically hostile terrain of the Assam–Arakan basin near fore deep of Himalayan foot hills is one of the key factors for hydrocarbon exploration among the Geoscientists. The area of study primarily falls close to the foot hills of Himalaya i.e. fore deep region in the North–East and partly in Belt of Schuppen (thrust belt) to the south-east, facing the Upper Assam foreland shelf in India. In such a complex mountainous and thrusted terrain, the seismic method has its own limitation to map the deeper geological basement configuration, because energy transmission is very meager and most part of the energies engrossed at boulder-sandstone formation. To overcome this problem it is always recommended to utilize some passive geophysical methods to supplement some value added constraints information to seismic data. Oil India Limited (OIL) decided to acquire ground Gravity-Magnetic (GM) as well as Magneto-Telluric (MT) data acquisition simultaneously in the fringe of Seismic lines where few profiles fall on the vicinity area to map the deeper subsurface information and also to make out the potentially hydrocarbon prospect zone. Additional quantitative spectral analysis technique has been used to map the top sedimentary layer and basement structure. This paper describes the correlation between GM, MT and Seismic data to map the different sedimentary layers and the basement configuration.


Imaging subsurface geological features with seismic migration – A numerical study
Department of Applied Geophysics, Indian School of Mines, Dhanbad – 826 004
E.mail: priyamohanty@hotmail.com

The seismic data recorded at the surface are processed in a complex sequence of steps among which seismic migration plays an important role. This paper presents an overview of the Phase Shift (PS) and Phase Shift Plus Interpolation (PSPI) wave equation migration methods applied to various geological models. PS time migration and PSPI depth migration schemes are applied to a syncline, anticline, graben and complex salt dome structures. It is observed that the PSPI migration method works well for all the structures in terms imaging and accuracy as compared to PS migration.

Empirical relation for estimating shear wave velocity from compressional wave velocity of rocks

R.S.Wadhwa, N.Ghosh and Ch.Subba Rao
Central Water and Power Research Station, Khadakwasla, Pune – 411 024
E-mail : wadhwa_rs.cwprs@nic.in

In situ shear wave velocity is one of the most important parameters for evaluating dynamic elastic moduli and needs special energy sources for generation and receivers for detection. Identification of shear wave phase on a seismic record needs skill as it is not the first wave to arrive and is usually embedded in surface waves. To estimate shear wave velocity for site characterization and for predicting the in situ quality of rock, empirical relations were proposed by Carroll (1969) to predict shear wave velocities from compressional wave velocities of rock samples. His empirical relation was used on the actual field data and the estimated shear wave velocities were compared with in situ velocities measured using cross-hole seismic technique. The shear wave velocities measured at four nuclear power plant sites were used to generate the correlation between compressional and shear wave velocities. A power fit model with a regression coefficient of 0.84 was developed. This correlation is valid for rocks having compressional wave velocity ranging from 4000 m/sec to 6000 m/sec and Poisson’s ratio between 0.22 and 0.28. The proposed relation is based on 185 data pairs of in situ compressional and shear wave velocity measurements conducted at four nuclear power project sites. The sites with different host rocks are: Kota (Rajasthan), Kaiga (Karnataka), Tarapur (Maharashtra) and Kakrapar (Gujarat). The empirical relationship proposed in this paper is first of its kind in India. The proposed empirical relation can be used to predict shear wave velocities at similar rock sites anywhere in India.

Interlinking of River Basins: A Mega Harvesting Plan-A Review
B.S.Prakasa Rao, P.H.V.Vasudeva Rao, G.Jaisankar, E. Amminedu, M.Satyakumar1 and P.Koteswara Rao2
Department of Geo-Engineering, College of Engineering, Andhra University, Visakhapatnam - 530 003
1 Meteorological Center, Begumpet Airport, Hyderabad - 500 616
2 National Geophysical Research Institute (CSIR), Uppal Road, Hyderabad - 500 606
E-mail: bosukonda@rediffmail.com, msatyak@yahoo.com

Water availability is becoming dearer and dearer day by day in India due to monsoon vagaries and increasing population propulsion. Linking of basins through canals is not a new concept, but has been in practice since times immemorial. Inter-basin water transfer was primarily envisaged by Rao and Dastur in 1970s. The President of India, Abdul Kalam gave a shot in the arm early in 2003 to the issue of linking of rivers. Ultimately the National Water Development Authority (NWDA) made thorough study, which indicated that Himalayan Rivers, have exceedingly surplus quantum of water and hence, proposed transfer of water from these surplus basins to deficit basins in peninsular region. We opine that the areas of dry land to be converted into a wetland, and the areas of unproductive land to be converted into agriculture land are far more than the land to be lost due to canals and reservoirs. Moreover, increase in the number of crops per year or the cropping intensity also increases along the link canals and the rivers to be linked. It is an environmentally sound and sustainable, technically feasible and socially acceptable measure, also to control inundation and floods through dense afforestation of the river banks. It reduces siltation too. Thus, the economic and ecological benefits far outweigh the feared losses.



Study of ionospheric variability during geomagnetic storms
Rakhee Malik, Shivalika Sarkar, Shweta Mukherjee and A.K. Gwal

Space Science Laboratory, Department of Physics, Barkatullah University, Bhopal - 462 026
Email: sslakg@gmail.com

The dual frequency Global Positioning System (GPS) receivers provide an opportunity to determine Total Electron Content (TEC) over the crest of equatorial ionization anomaly region Bhopal by taking advantage of the dispersive nature of the ionospheric medium. The TEC values observed for eight geomagnetic storms of the period 2004-2005 is used in this paper to discuss the behaviour of ionospheric total electron content (TEC) during geomagnetically disturbed periods. Variation of TEC is studied in correlation with the geomagnetic index Dst and southward component of interplanetary magnetic field Bz. The main purpose of this study is to know how TEC varies from its average values with geomagnetic storms. The TEC variability is found to vary between 49%-104% with the maximum negative excursion of Dst index during the geomagnetic storms days. Positive phases are observed for all the storms studied. Maximum TEC variability is observed during the recovery phase of the storms. The study of storm time TEC behaviour is very important due to recent increase in satellite-based navigation applications.



Weekly growing periods in extremities over India – monsoon period
A.A.L.N.Sarma and B.Sivaram1

Department of Meteorology and Oceanography, Andhra University, Visakhapatnam – 530 003
E-mail: aalnsarma_met@rediffmail.com.
1Birla Institute of Technology and Sciences, Pilani- Dubai, UAE.
Email: aalnsarma_met@rediffmail.com, sivaramboppe@yahoo.co.in.

India, being an agrarian country, the studies on Growing periods plays an important role in crop growth and performance in particular during the ocean atmospheric interactions such as ENSO/LNSO, which modulate the south west monsoon of India. The present paper addresses not only the growing period of India and selected stations from the Moist and Dry climates of India during the monsoon period of 1951-80, 1981-91, 1992-98, on a weekly basis, but also the affectivity of ocean atmospheric interactions such as ENSO/LNSO and SST of Nino 3 region for the ENSO year (1987) and LNSO year (1988) through the revised water balance model. The trend analysis of growing periods with respect to the march of SOI and SST of Nino 3 region for the period 1992-98 has been presented.


Rock magnetic and Palaeomagnetic Study of the Archaean Granites from Hyderabad, India
M.R.Goutham1, 2, R. Sandhya1, B. Madhusudhan Rao1, S.K. Patil2 and B.V.S.Murthy1

1Center of Exploration Geophysics, Osmania University, Hyderabad - 500 007
2Dr.KSKGRL, Indian Institute of Geomagnetism, Allahabad - 221 505

Samples from Hyderabad granitic region are studied for their rock magnetic and palaeomagnetic behaviour. There are considerable differences between the pink and gery granites in the rock magnetic properties such as Intensity of natural remanent magnetization (Jn), magnetic susceptibility (c) and Koenigsberger’s ratios (Qn) and indicates that these granites are of two different origins. Average values of NRM intensity, c and Qn are found to be 488 and 637 Am-1; 1689 and 1780; and 9 and 19.7 for pink and gray granites respectively. Two different mean palaeomagnetic directions were obtained for these rocks after af demagnetization which are D/I = 159o/-25o and 268o/-40o. The corresponding palaeomagnetic poles lie at 69S/160E and 8S/327E respectively. Based on the statistics former direction 159o/-25o is considered as the palaeomagnetic direction of Hyderabad granitic region.


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