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Volume 19 No.2 April 2015


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Slow Spreading Ridges of the Indian Ocean: An Overview of Marine Geophysical Investigations

K. A. Kamesh Raju*, Abhay V. Mudholkar, Kiranmai Samudrala

CSIR-National Institute of Oceanography, Dona Paula, Goa – 403004, India
*Corresponding author: kamesh@nio.org


Sparse and non-availability of high resolution geophysical data hindered the delineation of accurate morphology, structural configuration, tectonism and spreading history of Carlsberg Ridge (CR) and Central Indian Ridges (CIR) in the Indian Ocean between Owen fracture zone at about 10oN, and the Rodriguez Triple Junction at ~25oS. Analysis of available multibeam bathymetry, magnetic, gravity, seabed sampling on the ridge crest, and selected water column data suggest that even with similar slow spreading history the segmentation significantly differ over the CR and CIR ridge systems. Topography, magnetic and gravity signatures indicate non-transform discontinuity over CR and suggest that it has relatively slower spreading history than CIR. Magmatic and less magmatic events characterize CR and CIR respectively and well defined oceanic core complex (OCC) are confined only to segments of the CIR. The mantle Bouguer anomaly signatures over the ridges suggest crustal accretion and pattern of localized magnetic anomalies indicate zones of high magnetization coinciding with the axial volcanic ridges. Geophysical investigations / thermal plumes in the water column, have brought out two new hydrothermal vents over CR and one vent indication over the CIR. The analysis of the tectonic and magmatic character of the CR and CIR based on the available high resolution data suggests that both these slow spreading ridge sections have the potential to host high temperature active hydrothermal vents and need to be investigated by AUV and ROV experiments to identify the causative mechanism of these vents and their association with unique seafloor and sub-seafloor deep-sea ecosystems. These ridges hold great promise of mineral resources.


Aeromagnetic Analysis to Locate Potential Ground Water Zone - A Case Study from South Indian Shield

K.Satish Kumar*, R.K. Kishore, R. Raj Kumar, D.Seshu, V. Pradeep Kumar and Parveen Begum

CSIR-National Geophysical Research Institute, Uppal road, Hyderabad-500 007
*Corresponding Author: satish_marine777@yahoo.co.in

Analysis of total intensity Aeromagnetic anomaly image and the apparent susceptibility image of Eastern Dharwar Craton (EDC), in conjunction with hydrological and geomorphological data has resulted in delineating an hitherto un mapped fault structure. The occurrence of ground water in the study area is found to be controlled by E-W & NW-SE trending dykes. Spectral and quantitative analysis of the aeromagnetic data of the study area has indicated 150 m thick top layer associated with weathered and sheared granite gneissic terrain. This is a profitable zone for ground water exploitation.


Chirp Sonar and Electrical Resistivity Imaging survey for integrity of concrete lining in a Hydel Channel
M.S. Chaudhari*
Central Water and Power Research Station, Pune 411024, India
*Corresponding Author : mukund_chaudhari@yahoo.co.in

Underwater geo-engineering survey, deploying chirp sonar system (frequency modulated signal 500 Hz to 12 KHz) along with dual frequency echo-sounder from a precisely positioned vessel was carried out along one traverse of about 1.0 km length. The survey was aimed to assess the quality of concrete lining at the bed of Nangal Hydal Channel, which is an integral part of Bhakra Nangal dam located in border of Himachal Pradesh and Punjab. The channel has a bed width between 17 m and 24 m with a 2 m/sec velocity of water flow. The integrity of channel lining was identified by measuring reflection coefficient (R) values between water and channel bed interface. Different values for the reflection coefficient are obtained for concrete lined channel bed and the channel bed where concrete lining is disturbed. At the channel bed, the R value greater than 0.69 has been inferred to represent good to very good quality concrete and the places with R value less than 0.48 have been inferred as inferior quality concrete. Compressional wave velocities have been estimated from reflection coefficients and used to infer the quality of concrete. The reflection coefficient values of 0.48 and less observed in the seismic records from channel RD 2830 m to 2920 m revealed zones of inferior quality. Electrical resistivity imaging survey conducted along two profiles on the banks of the channel revealed a few zones of comparatively higher resistivity (205 Ω m - 700 Ω m). These zones located from channel RD 2898 m to 2948 m, with varying dimensions, are attributed to the zones prone to excessive seepage. It is inferred that water is getting leaked due to inferior quality of the concrete in the channel bed and is coming out from the adjacent banks of the channel, where the same is observed in ERI sections as high resistivity zones.

Diamond Prospectivity of Mesoproterozoic kimberlites from the Wajrakarur field, southern India: Perovskite oxybarometry and bulk-rock transition element geochemistry constraints
Debojit Talukdar and N.V.Chalapathi Rao*
Department of Geology, Centre of Advanced Study, Banaras Hindu University, Varanasi-221005
*Corresponding author: nvcr100@gmail.com

Prognostication of the primary diamond host rocks such as kimberlites and lamproites is traditionally carried out by deploying proven techniques such as indicator (xenocryst) mineral chemistry and pressure-temperature estimates on co-existing phases in mantle xenoliths. However, in the recent past new methodologies - such as estimation of redox nature of the magmas from perovskite oxybarometry and response of first-row transition elements to oxygen fugacity- essentially involving the bulk-composition of the host rocks have also emerged for predicting the diamond prospectivity. Here, we test the applicability of such host rock models to the well-characterized Mesoproterozoic kimberlites from the Wajrakarur field, eastern Dharwar craton, southern India, whose diamond incidence is well-established. We demonstrate that a combination of perovskite oxybarometry and transition element geochemistry in conjunction with petrography can impose better first order controls on the prognostication of the primary diamond host rocks rather than by applying them individually, in isolation. We also highlight that such a combined approach holds as much promise as the well-established and age-old prognostication techniques that are currently in vogue, for inferring the diamond prospectivity of the primary host rocks.

1-D velocity model delineated using dense seismic network in the Koyna-Warna region, Maharashtra, India
*Suman Kilaru 1,3, Sanjay Kumar 1, M.M.Dixit1 and P.Rama Rao2
1. CSIR-National Geophysical Research Institute (NGRI), Hyderabad, India.
2. Department of Geophysics, Andhra University, Visakhapatnam, India.
3. NCAOR-National centre for Antarctica and Ocean Research, Headland Sada, Vasco-da-gama, Goa
*Corresponding author: suman.geophy@gmail.com

For the first time in the Koyna-Warna region of Maharashtra state, India the CSIR-National Geophysical Research Institute, Hyderabad deployed a dense seismic network of 97 stations. They were operated for five months. A total of 499 earthquakes were located using SEISAN software. The Lithology indicator viz., the Vp/Vs ratio (Pickett 1963) was determined using the Wadati diagram and VELEST (Kissling et al. 1994). The results of the relationship established between Vp and Vs are then applied to delineate a 1-D P-wave velocity model using VELEST (Kissling et al. 1994) approach to solve hypocentral parameters. Analysis of data helped in delineating 1-D velocity structure, viz., 1) Exposed Deccan trap basalt of 1.2 km thickness with P-wave velocity (Vp) of 4.81 km/sec, 2) gneiss granitic basement layer with a thickness of 8.8 km and velocity (Vp) of 5.935 km/sec and 3) middle crust with velocity (Vp) of 6.355 km/sec. Middle crust is found to be extending to a depth of 25 km (thickness 15 km). Middle crust details have been taken from D.S.S derived velocity-depth model of Kaila et al (1979). Until , authentic teleseismic data from distances beyond ~50 km and extending to at least 100 km are utilized in building the velocity-depth model, we reiterate that it is not desirable to specifically use velocity- depth information (in the depth range10-25 km), from other studies for precise relocation of region`s earthquakes. The 1-D velocity (Vp) model, extending to 10 km, presently obtained significantly reduced RMS error and improved earthquake locations. We are confident about accuracy of improved earthquake locations, especially of the earthquakes having focal depths extending to not more than 10 km (The focii of Koyna- Warna earthquakes are generally found to lie between 3 to 7 km).

A Changes in the moment rate and the long term seismic deformation pattern: Before and after 26 Dec 2004 earthquake
Dept of Earth Sciences, Pondicherry University, Puducherry, India -605014
Corresponding author: lasitha_s@yahoo.com

A detailed analysis of changes in the long-term seismic deformation before and after the 26 December 2004 mega thrust earthquake shows that there is a drastic increase in the deformation rate and moment release in and around the region where the event have occurred. The partial compression with a component of strike-slip faulting is appeared to be transformed into a completely compressional environment due to the post-2004 earthquake seismic deformation in the Sumatran offshore. The calculated deformation velocities and moment release rate for the region between 1o to 5o N in the offshore Sumatra, is low prior to the mega earthquake, which suggest that strain have been accumulating in the area which has finally ruptured on December 2004. The estimated velocity values along the SFZ seismic belt indicate variation in seismically active deformation with maximum dextral shear motion of 29 mm/yr in the central part to 1 and 8 mm/yr both southward and northward respectively along the SFZ. Except between 0°-2°S, the estimated velocities are significantly less than the geologically estimated slip rates as well as geodetically measured slip rates which suggest that considerable amount of slip along the fault may be taking up aseismically. The Andaman arc also shows a low seismic deformation rate compared to the rates obtained from GPS observations indicating that earthquake data alone cannot be used to calculate short term slip. The vertical component of velocities suggests crustal thinning in the Andaman Sea and crustal thickening all along the fore arc.

Post stack inversion for reservoir characterization of KG basin associated with gas hydrate prospects
Bipasha Sinha and P. R Mohanty
Department of Applied Geophysics, Indian School of Mines, Dhanbad -826004
bipasha.agph.19@gmail.com, priyamohanty@hotmail.com

Post–stack inversion transforms a single seismic data volume into acoustic impedance through integration of seismic data and well data. Benefits of acoustic impedance obtained after inversion are well established for stratigraphic interpretation in comparison to conventional seismic data analysis. Model based and band limited post stack seismic inversion are carried out with a 2D seismic data to derive the stratigraphic information. The methodology of inversion includes statistical analysis of log derived acoustic impedance with P-wave velocity, density and spectral analysis of seismic data, wavelet estimation, seismic to well tie, generation of initial 2-D geological model. Use of model based inversion scheme and band limited inversion has validated inverted impedance results. Present study is based on data from Krishna Godavari basin of India. Model based and band limited inversion results have helped in delineating the stratigraphic prospect in the study area. This study demonstrates the effectiveness of using acoustic impedance volume for performing stratigraphic interpretation and reservoir characterization. From this study, it is noticed that near vertical reflection two way time 250 ms to 350 ms with CDP 630-700 have high acoustic impedance contrast, which can be interpreted as potential gas hydrate saturated zone.

Importance of atmospheric dust in India: Future scope of research
UC Kulshrestha* and Disha Sharma
School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067 INDIA
*Corresponding Author:umeshkulshrestha@gmail.com

Abundance of soil-dust in Indian atmosphere is a natural geo-engineering tool to combat acidification and climate change. Local as well as transported dust contributes to very high loadings of particulate matter which often exceeds the prescribed limits. Alkaline nature of atmospheric dust acts as a scavenger of SO2 and hence, SO2 concentrations are not recorded very high in the ambient air in India. Also, atmospheric dust affects radiative forcing, cloud modification and heath of humans and plants in Indian region. This report highlights that in spite of its great regional importance, investigations about various aspects of atmospheric dust e.g. budget and inventory, long range transport and sources, combined characterization of carbon mixed aerosols and their role in radiative forcing and monsoons need dedicated  systematic research efforts.

Navigational Electronics Present Status, Future Demands and Strategies to Enhance Quality
Dept.of ECE, CBIT, Hyderabad,
Former Director, Research and Training Unit for Navigational Electronics, Osmania University, Hyderabad

This paper briefly discusses history of navigation followed by operating principles of various satellite based navigations systems. The limitations as well as performance enhancement techniques are mentioned. The present status of satellite based navigation systems is discussed. The importance of latest techniques including indoor navigation and source localization are highlighted. The major future demands and strategies to enhance quality are given.

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