Archived Issue

May, 2016   ||  Volume 20 No.3

Editorial


1
Estimation of gas hydrate saturation using model based acoustic impedance inversion from Mahanadi offshore basin

Uma Shankar*1, Debjani Bhowmick2 and Kalachand Sain3
1Department of Geophysics, Institute of Science, Banaras Hindu University, Varanasi-221005
2CMPDI (HQ), Kanke Road, Rachi-834008
3CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad – 500007
*Corresponding Author : umashankar_ngri@yahoo.com

 ABSTRACT
The bottom simulating reflector (BSR), observed on seismic section in the Mahanadi offshore basin indicates the presence of gas hydrates. Gas hydrate saturation is estimated from electrical resistivity log based on Archie’s empirical relation and/or from sonic velocity log using rock physics modeling approach at the vertical log position. The lateral and vertical extent of gas hydrates saturation over a larger area is obtained by post-stack impedance inversion of seismic data constrained by well log data. The inverted velocity coupled with rock physics modeling provides the estimation of gas hydrate saturation. The present study suggests that average gas hydrate saturation along a seismic line passing through site NGHP-01-19 in the Mahanadi Basin is about 3%. Gas hydrate saturation directly measured from the pressure cores, is found to be 2.4% at site NGHP-01-19, showing close correspondence with the estimation.
Key words: Gas hydrate, Acoustic velocity, Acoustic impedance inversion, Gas hydrate saturation.



Global Seismic Temporal Pattern and Enhanced Seismicity Since 2000

B. K. Rastogi and Jyoti Sharma*
Institute of Seismological Research (ISR), Department of Science and Technology
Government of Gujarat, Village - Raisan, Gandhinagar, Gujarat - 382009, India
*Corresponding Author: jyotisharmaiitkgp@gmail.com

ABSTRACT
Temporal pattern of global seismicity indicates temporal clustering of large earthquakes (Mw≥8.2) followed by relative quiescence (stress shadow). It is a characteristic seismic pattern along the plate boundaries. Clustering of the largest earthquakes during 1950s to 1960s followed by the extended period of low-moment release until 2003 and then again heightened moment release since 2004 has been observed, which represents a seismic temporal pattern of 50 years period. Similarly, the Alpine-Himalaya-Andaman-Sumatra (AHAS) belt and stable Indian Peninsular region have showed repeated temporal pattern of high and low seismicity. In the AHAS belt, seismicity was high during 1897 to 1916, low during 1917 to 1933, high again during 1934 to 1951, low again during 1952-1999 and since 2000 onwards seismicity has again enhanced. It has been observed that when there were no great earthquakes in Himalaya, the Peninsular India experienced, during that period, more number of M≥6 earthquakes.
Key words: Seismicity, Clustering, Quiescence, Temporal pattern.



A statistical study of TEC anomalies induced by major earthquakes occurred around Indian Subcontinent

Devbrat Pundhir*1,3, Birbal Singh1, O. P. Singh2 and Saral Kumar Gupta3
1Department of Electronics & Communication Engineering, R. B. S. Engineering Technical Campus, Bichpuri, Agra, India-283105
2Department of Physics, R. B. S. Engineering Technical Campus, Bichpuri, Agra, India-283105
3Department of Physics, Banasthali Vidyapith, Banasthali, Rajasthan, India-304022
*Corresponding Author: devbratpundhir@gmail.com

ABSTRACT
The GPS based TEC measurements have been in progress at Bichpuri, Agra station (27.2o N, 78o E) in India since 1 April 2006 using a dual frequency GPS-receiver. In the present paper, we analyze the TEC data for the period of April-September 2013 to examine the anomalous variations as precursors corresponding to some major earthquakes (M > 6) that occurred during this period in the Indian subcontinent. We processed the data using well known mean (m) and standard deviation around the mean (σ) criterion to see the anomalous variations as precursors in the form of enhancements above the upper limit (m + σ). Then we found the correlation coefficients between magnitude of earthquakes and precursory days and average TEC enhancement, respectively. We found significant correlation coefficients in the two cases. Finally, we tested the null hypothesis for pairs, which have the maximum and minimum values of correlation coefficients. In this way, the precursory days and corresponding TEC anomalies are fixed for the earthquakes. The concepts of E × B drift mechanism and Global Electric Circuit (GEC) are invoked to explain the ionospheric precursors of earthquakes.
Key words: Multiple earthquakes; GPS-TEC; correlation coefficients; null hypothesis; E × B drift; Global Electric Circuit (GEC) .


Structural Inferences from Radiometric Surveys in and around Ramadugu Lamproite Field, NW margin of the Cuddapah basin, Eastern Dharwar craton 

G.Sri Ramulu, G.Ramadass and B.Veeraiah*
Center of Exploration Geophysics, Osmania University, Hyderabad-500 007, India
*Corresponding Author: veer.cegou@gmail.com 

ABSTRACT
An attempt has made to map radiometric intensity over a part of the Ramadugu, Vattikod, and Somvarigudem lamproite fields of Nalgonda District, Telangana State, North Western margin of the Cuddapah basin and their relationship with geological structures and tectonics.
Interpretation of radiometric data brought out the structural features, trends, faults and contacts corresponding to the lithological formations observed in the area. The formations are amphibolites, schists, biotite gneisses, granites, granodiorites and dolerites. They are qualitatively inferred from the radiometric map, which may enable more precise geological mapping of these formations. A geological map of the study area with observed radioactivity of each formation is presented. The corresponding radioactivity for amphibolites, schist, biotite gneiss, granites, granodiorite, quartz vein and dolerites are 23.15 µR/hr (22.87 µR/hr to 23.4 µR/hr), 22.77 µR/hr (20.94 µR/hr to 24.8 µR/hr), 27.69 µR/hr (20 µR/hr to 37.05 µR/hr), 25.62 µR/hr (24.77 µR/hr to 27.7 µR/hr), 20.85 µR/hr (15.69 µR/hr to 23 µR/hr) and 26.5 µR/hr (12.38 µR/hr to 40.71 µR/hr), respectively. A low radioactivity has been registered over Ramadugu lamproite field (18.25 µR/hr to 21.58 µR/hr) and Yacharam lamproites field (19.91 µR/hr to 20.41 µR/hr), Vattikod lamproites field 25.56 µR/hr to 27.82 µR/hr ) and Somavarigudem lamproites field ( 17.38 µR/hr to 18.13 µR/hr) .
Coefficient of variation values calculated for the radiometric data revealed seven deep-seated faults (F1 to F7), two running NW-SE, three NE-SW, one N-S and one another NNW-SSE. In addition, radiometric data revealed in the region disposition of schist belts, various faults and other lineaments /dykes and contact between granite gneiss and dolerite dykes.
Key words: Radiometric surveys, Lamproite field, clusters, enclaves and Geological structures.



Red beds in the Cuddapah Basin, eastern Dharwar craton, India: Implications for the initiation of sedimentation during the Proterozoic Oxygenation event

V. V. Sesha Sai*1, Tarun C. Khanna2 and N. Rama Krishna Reddy3
1Petrology Division, Geological Survey of India Training Institute, Hyderabad - India
2CSIR-National Geophysical Research Institute, Hyderabad – 500 007, India
3Loyola Degree College (YSRR), Pulivendula, Andhra Pradesh – 516390, India
*Corresponding Author : seshubb@yahoo.co.in

ABSTRACT
Based on the field, petrological and geochemical studies we make a detailed report on the occurrence of Proterozoic red beds from the intra-cratonic Cuddapah basin of South India. Studies in old Kadiri Ghat – K. K. Kottala section in SW part of the Cuddapah Basin indicate the presence of extensive red bed sequence with varied mineralogical, textural and lithological composition forming part of the Gulcheru Formation in the Paleoproterozoic Cuddapah Super group. Studies further reveal that a greater part of the clastic sedimentary rocks from the lowermost Gulcheru Quartzite of Papaghni Group to Bairenkonda Quartzite of Nallamalai Group are ferruginous. The present studies also highlight the existence of a thick sequence
(~ 400 m) of ferruginous lithic arenite interbedded with a non-clastic reddish jasper and dolomite sequence in the middle part of Tadpatri Formation of Chitravathi Group in Mallela section and an iron oxide rich ferruginous siltstone (with 37 % Fe2O3) in lower part of Bairenkonda Quartzite in Nandyal-Nandikanuma pass section of Nallamalai Group. An age of 1.9 Ga for the mafic-ultramafic sill emplacement in Tadpatri Formation within the Chitravathi Group of Cuddapah Supergroup indicates the age of deposition of the host sediments to be older than this date. Considering the 1900-2000 Ma age of Vempalle dolomites, it is inferred that the Gulcheru red beds were deposited around 2.1 Ga; a period that corresponds to the global oxygenation event and a period that witnessed deposition of red beds in the platform type of Proterozoic basins in the world.
Key words: Red beds, Proterozoic Cuddapah basin, Eastern Dharwar Craton, Sedimentation, Oxygenation event.



Grain Size Distribution of Coastal Sands between Gosthani and Champavathi Rivers Confluence, East Coast of India, Andhra Pradesh 

Bangaku Naidu, K.,* Reddy, K.S.N., Ravi Sekhar, Ch., Ganapati Rao, P., and Murali Krishna, K.N.
Department of Geology, Andhra University, Visakhapatnam-530003
*Corresponding Author: naidu0756@gmail.com

ABSTRACT
The studies on grain size characteristics are valuable to understand the source for the evolution of coastal sand environments. Seventy one sediment samples from twenty traverses of costal sediments in between Gosthani River mouth in south and Champavathi River in the north (Lat.17º52'-18º.02' N; Long.83º26'- 83º36' E) have been collected and studied. The coastal sediments are medium to fine grained (1.68 Ø – 2.80Ø), very well sorted to moderately well sorted (0.26Ø – 0.67Ø), strongly coarse to fine skewed (-0.63 Ø to 0.31Ø) and pltykurtic to leptokurtic (0.74Ø – 1.27Ø) in nature and deposited in moderate to high energy environment conditions with dominant rolling, bottom and graded suspension mechanisms. The observations are supported by the frequency distribution curves, CM plots and scatter plots between parameters, conforming to the bimodal nature to dominant fine sand in different microenvironments (dune, backshore, berm, and foreshore). These textural parameters have been further examined to understand the hydrodynamic conditions of the depositional environments.
Key words: Textural parameters, coastal sands, coastal sediments, Dune, Backshore, Berm, Foreshore, Gosthani and Champavathi rivers


7

- A technical report
Unusual lightning activity over Andhra Pradesh and Telangana on 6 September, 2015: A Report 

Kamaljit Ray1, S.C. Bhan*1 and S. Stella2
India Meteorological Department, 1New Delhi, 2Chennai
*Corresponding Author: scbhan@gmail.com


8

Research Note
Lithological Characteristics Analysis of Ridderkerk Area in the Western Netherlands using Wavelet Transform 

Soumya Chandan Panda*1, Sankar Kumar Nath1 and Niva Brahma2
1Department of Geology & Geophysics, Indian Institute of Technology, Kharagpur
2Department of Applied Geophysics, Indian School Of Mines, Dhanbad
*Corresponding Author: scpagp@gmail.com

ABSTRACT
Various wavelet transform techniques have been used for delineating lithological boundaries and to provide subjective leads for reservoir characterization. A multi-scale analysis of the well log data was performed using both the Continuous Wavelet Transform (CWT) and Discrete Wavelet Transform (DWT) analyses. The gamma ray log was first DWT analyzed using the Haar Wavelet and decomposed 7 times. The discrete coefficients pertaining to the 7th level of decomposition were CWT analyzed using the Haar Wavelet at various scales ranging from 2-10 m, 10-20 m, and 20-100 m and the results of the analysis have been presented. This study demonstrates that Wavelet Transforms can effectively be used for bed boundary detection as a first approximation, as demonstrated through the comparison with the facies log presented. This technique can, therefore, be used cost-effectively in a short time span for valuable resource delineations in Geoexploration.
Key words: Lithological characteristics, wavelet transform, gamma ray log, Ridderkerk, western Netherlands.


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