January, 2015

January, 2015   ||  Volume 19 No.1



Exploring the Passive Margins–a case study from the Eastern Continental Margin of India


Former CSIR Emeritus Scientist, Presently MoES Project Scientist, CSIR-National Institute of Oceanography,
Regional Centre, 176, Lawsons Bay, Visakhapatnam. 530017


The Eastern Continental Margin of India (ECMI) is a passive margin, evolved due to the break-up of India from East Antarctica during Late Cretaceous (140–120 Ma). Over the last three decades extensive marine geophysical data (bathymetry, magnetic, gravity and multi-channel seismic reflection) was collected over the ECMI. These data sets were analyzed to understand the structure, tectonics and the geodynamic evolution of this passive margin.
This paper presents the synthesis of the results obtained from marine geophysical studies spanning over a period of nearly two decades, mainly related to the geomorphology, tectonics, coastal seismicity, Holocene sea level history and marine geohazards of the margin. The geodynamic evolution of this passive margin is explained based on the major tectonic lineaments like Continent-Ocean Boundary (COB), the NE-SW horst and graben trend of the continental basement and the rift related dyke intrusions within the continental basement. Land – Ocean Tectonic lineaments (LOTs) identified from the data reveal neotectonic activity associated at the three locations over the ECMI. Holocene sea level history has been traced from the high resolution seismic reflection data. Marine geohazards over the basinal and non basinal areas of ECMI have been demarcated. Scope for future studies is also discussed.


Geoelectrical investigation for potential groundwater zones in parts of Ratnagiri and Kolhapur districts, Maharashtra

*Gautam Gupta1, Vinit C. Erram1 and Saumen Maiti2

1Indian Institute of Geomagnetism, New Panvel (W), Navi Mumbai 410 218
2Dept. of Applied Geophysics, Indian School of Mines, Dhanbad 826004
*Corresponding Author: gupta_gautam1966@yahoo.co.in

Study of significant variations in nature and extent of weathering due to the presence of fractures and lineaments at depth and the geomorphological features at the surface is vital for groundwater exploration in a hard rock terrain. An attempt is made here to understand the vertical distribution of water bearing zones in the shallow formations over Devrukh-Ganapati Pule and Malkapur-Ratnagiri sections through geoelectrical studies. Two-dimensional geoelectrical cross-sections along five profiles reveal potential aquifer zones at a few sounding locations viz. 1, 2, 4, 5, 6, 7, 17, 18, 20, 21 and 22 with resistivities varying from 22-36 Ω-m over Devrukh- Ganapati Pule profile. Potential aquifer zones are also revealed at sounding points 24, 25, 34, 37, 39, 40, 41 and 42 in the eastern part of the Malkapur-Ratnagiri profile in the resistivity range of 22-37 Ω-m. Several lineaments cris-crossing this region play a significant role in the occurrence and movement of groundwater as revealed by low resistivities near VES 6, 5, 4, 16 and 17 over Devrukh-Ganapati Pule profile and VES 24, 25, 34 and 37 over Malkapur-Ratnagiri profile.


Structure and evolution of Satpura Gondwana Basin over Central Indian Tectonic Zone: inferences from seismic and gravity data
Jyoti Singh1,2, K. Chandrakala1, *A.P. Singh1 and D.M. Mall1
1CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad-500007
2Oil and Natural Gas Corporation Ltd., Kaulagarh Road, Dehradun-248195
*Corresponding Author: apsingh@ngri.res.in

Satpura Gondwana Basin is located over the Pachmarhi plateau of Central Indian Tectonic Zone (CITZ) in central India. Its exposition at an unexpected height of 900 m above the granite-gneiss basement rocks encompassing the Pachmarhi plateau distinguishes it from other Gondwana basins of peninsular India. The complete Bouguer anomaly map of the region is characterized by a broad relative gravity low over Satpura Gondwana Basin and high over the CITZ as compared to the adjoining regions. 2½-D gravity modelling across the Satpura Basin, constrained by deep seismic sounding and available well log data, was carried out. Our study establishes more than 5 km thick Gondwana sediments deposited in a fault controlled basin and high density Palaeoproterozoic Mahakoshal belt as a horst along the Precambrian suture between the CITZ and the Bundelkhand craton. Our results also support the earlier studies that have suggested probable presence of about 5 km thick Mesoproterozoic Vindhyan sediments, believed to have been deposited on the southern margin of Bundelkhand Craton as a foreland basin during the convergence phase. Besides a high density (2.91 g/cm3) mid-crustal body, a velocity (6.50 km/s)/density (2.91 g/cm3) layer at the base of the crust and relatively lower velocity (7.9 km/s)/density (3.22 g/cm3) subcrustal mantle are also delineated beneath the region. Complex crustal structure with anomalous velocity/density layers beneath the CITZ suggests probable magmatic underplating due to Deccan volcanism. It is suggested that the Satpura Gondwana Basin, formed as drop down basin over the CITZ, could have been finally uplifted to its present height by the late Cretaceous Deccan volcanism.

Deciphering the seismicity pattern from MEQ study atIndira Sagar reservoir area, Madhya Pradesh, India.
G.Dhanunjaya Naidu*, Sachin Khupat and D.K.Awasthi
Central Water and Power Research Station, Pune
*Corresponding Author: dhanugeo@gmail.com

Indira sagar reservoir, one of the largest reservoirs ofthe country located in seismically active Central India Tectonic Zone (CITZ), witnessed significant seismic activity sincerecent past. Seismicity monitoring began in 1995 to study the local seismicity in and around the reservoir site, and it is being continued till today. Impoundment started in 2003 and seismicity of the region has been studied for the period of 1995-2009 with the help of microearthquake data by ten seismic observatories.The results of seismological investigations have facilitated in assessing seismic potential of the area and its possible impact on the dam. In addition, role of crustal scale seismotectonic features in triggering the seismicity is assessed with the help of magnetotelluric (MT) study. MT study delineated the major geological formations and fault features, which are responsible for seismic activity in the proximity of the reservoir. A total of 16 seismic events have been identified within the 50 km radius from the dam site with hypocentral depths of <15 km during study period of 1995-2009. Seismicity was found to be decreasing after water impoundment in the reservoir, contrary to reservoir triggered seismicity. Reduction in seismic activity indicates that seismicity may not be associated with reservoir dynamics.It is interpreted that seismicity of the regioncould be associated withlocal adjustments in the crustal blocks along a series of parallel gravity faults towards north and south of the Narmada Riverand other existing seismogenicfaults near the dam site. Seismicity,as a whole,is inferred as due to regionaltectonic forceswithin the Central India Tectonic Zone (CITZ) and reservoir has little impact.

Movements of western disturbance and associated cloud convection
*Ramesh Chand and Charan Singh
India Meteorological Department, Mausam Bhavan, Lodi Road, New Delhi-110003
*Corresponding Author: r58.chand@gmail.com

Western disturbances have a long history of climatological, synoptic and satellite observations based studies. In present study an attempt has been made to understand the different aspects of western disturbances like movement, associated convection, induce systems and associated weather. The western disturbances (WDs) during post monsoon and winter season have been selected for the study as they are mainly responsible for precipitation over western Himalayan region and adjoining plains of northwest India. The areal extension of precipitation increases, in cases when westerly trough or WD interacts with southwesterly winds from Arabian Sea and easterly/southeasterly from Bay of Bengal. It caused rain/snow over western Himalayan region and rain/thundershowers with sometimes hailstorm over northern plains.
In present study 10 recent cases of WDs have been analyzed in detail to comprehend the characteristics of WD’s. Study revealed that the normal movement of the mid-level westerly trough (WD) is about 440 km/day i.e. longitude 4.50 day-1.In general WDs moves faster in case of typical synoptic situations like low pressure area or a cyclonic circulation ahead of the system in lower tropospheric levels. In case of slower moving WDs, it was observed that ridge/anticyclone is ahead of the system in lower levels. The maximum convection associated with westerly trough is located in an average 1200 km ahead of the westerly trough and coldest pixel north-east of the southern tip of the westerly trough. In general the cloud top temperature associated with western disturbances ranges from-40.0 to -60.00C. It is also observed that the WDs become intense when southern end of the trough in mid-level westerlies dips up to Arabian Sea.

A study of ionospheric precursors associated with the major earthquakes occurred in Pakistan region
*Devbrat Pundhir1,2, Birbal Singh1, D. R. Lakshmi3 and B. M. Reddy4
Department of Electronics & Communication Engineering, Raja Balwant Singh Engineering Technical Campus, Bichpuri, Agra, India-283105,
2Department of Physics, Banasthali Vidyapith, Banasthali, Rajasthan, India-304022
3Navigation Institute of Research and Training Unit, Osmania University, Hyderabad, India
4National Geophysical Research Institute, Uppal Road, Hyderabad, India
*Corresponding Author: devbratpundhir@gmail.com

The GPS-TEC measurements have been in progress at Agra station (27.2o N, 78o E), India since 01 April 2006. In the present paper, we analyze the GPS-TEC data for two months of April and September, 2013 in which two major earthquakes (M > 7) occurred in the adjoining region of Pakistan. We use the quartile based statistical technique for the analysis of data and identify the significant precursors associated with the earthquakes. These precursors occurred on different days in the interval of 2-10 days prior to the earthquakes. We also examine the effect of geomagnetic storms on the total electron content (TEC) data and find that the precursors are not influenced by the storms. The cause of the precursors is E × B drift with the electric field generated over seismic regions and penetrated the ionosphere.

A short note on the application of Singular Spectrum Analysis for Geophysical Data processing
*Rajesh Rekapalli and R.K.Tiwari
CSIR-NGRI, Hyderabad-500007, India
AcSIR-NGRI, Hyderabad-500007, India
*Corresponding Author: rekapalli@gmail.com

Singular Spectrum Analysis (SSA) is a popular time series analysis tool. Numerous studies have proven its efficacy in processing the data contaminated with various kinds of noises. As the geophysical field observations are highly non-linear and contains random as well as coherent noises, the analysis of data using SSA provides the significant information in terms of Eigen properties of the system under investigation. Unlike standard Fourier and wavelet methods, the basis functions of the SSA are completely data adaptive (Eigenvectors of trajectory matrix). Such data adaptive basis functions enable the self similarity of time series in data gap filling and noise suppression. Here we made an effort to briefly discuss the principal component analysis,frequency filtering, noise suppression and data gap filling of SSA and their application in time domain geophysical data processing.

Sustainability or Resilience: Need of the Hour: A Debate
*P. R. Reddy
Scientist (Retd), CSIR-NGRI, Uppal Road, Hyderabad- 500 007

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