Archived Issue

January, 2016   ||  Volume 20 No.1


Shallow surface shear wave velocity beneath the Godavari Rift using P wave seismograms of local earthquakes

K. Sushini 1, M. Ravi Kumar 1, B. Padma Rao 1,2 and G. Srijayanthi *,1

1 CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad, INDIA
2 Academy of Scientific and Innovative Research, CSIR-NGRI, Uppal Road, Hyderabad, INDIA
*Corresponding Author :

The prolonged micro to moderate sized earthquakes in the Indian peninsular shield over the past few decades have been linked with the rift zones and reactivation of pre-existing weak zones. The Godavari Rift is one such active rift situated in the southeastern part of the Indian shield. Moderate tectonic activity and presence of thick sedimentary deposits in this region accentuates the vulnerability due to earthquakes. Since the thick sedimentary layers and low shear wave velocities play a critical role in amplification of seismic waves even from small magnitude earthquakes, determination of shallow shear wave velocity (SSV) assumes importance. In the present study, shear wave velocities in the shallow subsurface are estimated adopting a latest technique that utilises the horizontal to vertical ratios of the local P waves. Our results indicate that the shallow subsurface structure is quite variable in the Godavari Rift, with the SSV values ranging between 3.22 km/s and 1.03 km/s. The SSV values obtained in the present study beneath different seismic stations are found to be in good agreement with the near surface velocities obtained from the receiver function technique using teleseismic P waves.
Key Words: Godavari Rift, Shallow surface shear wave velocity, Horizontal to vertical ratios, Local P waves.

New structural facts from audio-magnetotelluric (AMT) data interpretation in the Yaoundé-Nkolafamba area (Centre Cameroon)

S. P. Assembe 1, T. Ndougsa-Mbarga *1,2 and A. Meying 3

1 Postgraduate School of Sciences, Technologies & Geosciences, University of Yaoundé I, P.O. Box 8251, Yaoundé, Cameroon
2Department of Physics, Advanced Teachers’ Training College, University of Yaoundé I, P.O. Box 47 Yaoundé, Cameroon
3 School of Geology, Mining and Mineral Processing, University of Ngaoundéré, Cameroon
*Corresponding author:

Several geological models that explain the tectonic evolution of the Central Africa Pan-African Belt are discussed, each one having both outstanding results and unresolved questions. To improve the knowledge of the Pan-African domain in Cameroon, especially within the Yaoundé series, a geophysical investigation of shallow crustal structures was carried out in Nkolafamba, 26 km away from Yaoundé on the Yaoundé-Akonolinga highway, between the northing latitudes 03°45 and 04°, and easting longitudes 11°30 to 12° area during August 2011. The study combines field geological observations with twenty-three tensor Audio-magnetotelluric/Controlled source audio-magnetotelluric (AMT/CSAMT) experiments along four north 135° trending profiles, using a Geometric’s Stratagem EH4 resistivitymeter. The 2D modelling of geophysical data exhibits: (1) That the formations encountered in the area are a mixture of both Pan-African and Congo Craton formations; (2) Many folding patterns and a set of strike-slip conductive faults and fractures that correlate the field observations. From the outcome of the study, we state that the study area belongs to the transition zone between the Congo Craton and the Pan-African belt. We propose that many of these faults form a southwest-northeast shallow tectonic line, seem to be related to the enhancement of the Centre Cameroon Shear Zone within the Yaoundé area. These facts demonstrate that the region has been affected by the collision between the Pan-African and the steady Congo Craton, followed by post Pan-African transpressional evolution characterized by dextral and sinistral strike-slips along the southwest-northeast trend. Therefore, we opine that the indentation tectonics model, earlier proposed through some geological studies, is more suitable in describing the geological evolution. It is also evident that geophysics played significant role in better understanding of the Yaoundé series’ structural geology.
Keywords: Tensor audio-magnetotelluric experiment, Controlled source audio-magnetotelluric experiment, 2D modelling, tectonic line, Pan-African belt, Congo Craton, Yaoundé series.

Magnetic Fabric and Rockmagnetic Properties of the Archaean Granites from part of the Hyderabad Granitic Region (HGR), Eastern Dharwar Craton, India

M.R. Goutham*1, R. Sandhya2, S.K. Patil3, B. Madhusudhan Rao2 and B.V.S.Murthy2
1 Department of Geology, Government College [A], Rajahmundry 533105
2Center of Exploration Geophysics, Osmania University, Hyderabad 500 007
3Dr.KSKGRL, Indian Institute of Geomagnetism, Allahabad 221505
* Corresponding Author:

Archaean granite samples, collected from unweathered basement from part of the Hyderabad Granitic Region (HGR) consisting of pink and grey varieties, are studied for their magnetic fabric and rock magnetic characters. Rock magnetic properties show wide range of characters for both the varieties and grey granite is found to be more magnetic than the pink variety. Average values of Natural Remanent Magnetization (NRM) intensity, Magnetic Susceptibility (K) and Koenigsberger’s ratio (Qn) are found to be 488 and 637 Am-1; 1689 and 1780; and 9 and 19.7 for pink and grey granites respectively. There are significant differences in the rock magnetic properties between the pink and grey granites such as NRM Intensity, magnetic susceptibility (K) and Qn. Probably this is an expression of grade of metamorphism that these rocks have undergone and thus may be attributed to the time difference in their formation. The magnetic mineralogy of the granites of the study area is dominated by multi domain magnetite as revealed by the Isothermal Remanent Magnetic (IRM) and thermo magnetic studies. Further, the fabric of the magnetic minerals shown by both pink and grey granites is similar. This indicates that the deformation recorded in these rocks is a wide spread, post-formational event in the Eastern Dharwar Craton (EDC) and is exactly preserved in the Hyderabad Granitic Region (HGR).
Key Words: Natural remanent Magnetisation, Anisotropy of Magnetic Susceptibility, Koenigsberger`s ratio, Isothermal Remanent magnetization, Thermo magnetism, Dharwar Craton, Hyderabad Granitic Region.

Interpretation of gravity Data from Kutch (India), an intra-plate seismic region using scaling spectral method

A.R. Bansal*, V.K. Rao and V.P. Dimri
CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad – 500 007
*Corresponding Author: 

The gravity data of the highest seismic risk and tectonically complex region of Kutch (India) is analyzed using scaling spectral method along selected nine gravity profiles. The high-resolution multi-taper method (MTM) is used to calculate the power spectrum. The scaling spectral method provides scaling exponent and depth values, which are useful for describing the heterogeneity of the region. The depth values vary from 1 to 7 km with deeper values in the northern and southern region. The depth values and scaling exponents indicate complex nature of the crust. The calculated β values indicate a heterogeneous shallow crust in the region.
Key Words: Intra-plate Seismicity, Bhuj earthquake, Kutch, Gravity Method, Scaling Spectral Method, Fractals..

Geochemistry and petrogenesis of mafic alkaline dike(s) to the east of Gadwal greenstone terrane: Implications for OIB – type magmatism in parts of the eastern Dharwar craton, India

Tarun C. Khanna*1, E.V.S.S.K. Babu1 and Guochun C. Zhao2,
M. Satyanarayanan1, A. Keshav Krishna1, S. S. Sawant1

1CSIR – National Geophysical Research Institute, Hyderabad – 500 007, India.
2Department of Earth Sciences, The University of Hong Kong, Pokfulam Road,Hong Kong.
*Corresponding Author:

The Dharwar craton of southern India hosts a well preserved association of Archean granite - greenstone terranes and Proterozoic mafic dike swarms. Hitherto, the mafic dikes reported from the Dharwar craton, regardless of their occurrence in the eastern or western sector, are either tholeiitic or picritic and invariably contaminated by the Archean upper continental crust. In continuance to the previous study, this paper provides a rare account on the petrogenetic aspects of a Paleo-proterozoic crustally uncontaminated mafic dike "Dike 3" of alkaline affinity. Geochemically the rocks are basaltic in composition and mineralogically consist of clinopyroxene (Ti-augite), Na-rich plagioclase (oligoclase-andesine) as major silicate mineral phases while titaniferous magnetite ± ülvospinel are the opaque mineral oxides. The samples are characterized by strongly fractionated rare earth element (REE) patterns with elevated light-REE (La/Yb)N ~10 and depletion in the heavy-REE (Gd/Yb)N ~2.5 consistent with a garnet signature. Geochemical modelling involving HFSE (Zr, Nb and Y) and REE indicates that the melts were generated by low degree (~3-4 %) partial melting of a garnet facies mantle. The geochemical attributes of this dike are identical to the Phanerozoic ocean island basalts (OIB). La/Nb and La/Ba ratios in these samples indicate their derivation from an asthenospheric source, similar to the source of modern OIB. In contrast to the OIB, the Gadwal Dike 3 is characterized by an anomalous depletion in Nb relative to La in a primitive mantle normalized trace element variation diagram. This characteristic feature resembles with the unusual EM 1-type OIB from the Cretaceous, Site 525A of the Walvis Ridge, South Atlantic Ocean. Consequently, the anomalous behavior of Nb in the Gadwal Dike 3 samples is attributed to the addition of a small amount (~2%) of ancient pelagic sediment recycled through an Archean subduction zone, in its mantle source. The occurrence of OIB-type magmas within the cratonic interior provide an essential link between the Archean sub-continental lithospheric mantle (SLM), and the EM1 mantle component in the Dharwar craton, India.
Keywords: Mafic dikes, Ocean island basalt, Sub-continental lithospheric mantle, Gadwal greenstone terrane, Dharwar craton.

Hydrogeochemical Investigations and Solute Transport Modeling of Polluted Coastal Aquifer

B. Venkateswara Rao*1, G. Srinivasa Rao2 and K. Mahesh Kumar3
1 Professor of Water Resources, Centre for Water Resources, IST, JNTUH
2 Dy. Ex. Engineer, RWS & S, Govt. of A.P.
3 Asst. Hydrologist, TSGWD
*Corresponding Author :

The study area is an inter stream region of the Pennar and Upputeru Rivers located in the Nellore district of Andhra Pradesh, India. The groundwater levels and samples are collected from 196 observation wells penetrating the near surface aquifer to prepare groundwater contour maps and to analyse the groundwater samples for various chemical parameters. Occurrence of saline water in certain localized pockets due to intensified aquaculture and occurrence of saline water along the coast due to sea water intrusion are verified by various ionic ratios like Ca+2/Mg+2, TA/TH, Na+/Na++Cl- and Cl-/CO3-2+HCO3-. The above investigations have revealed that all along the coast, with a strip width of 2 to 5 km, groundwater levels are below the sea level at a depth of 1 to 3 m, consequently, there is seawater intrusion with TDS concentrations ranging from 1500 to 3000 mg/l along this strip. Similarly, the TDS values were found to be as high as 5000 mg/l at a localized pocket at T.P.Gudur due to storing of sea water meant for aquaculture. In general, the seawater spreading is more during the pre-monsoon season and it is considerably diluted in the post-monsoon season due to recharging from Pennar river, Survepalli canal, tanks and precipitaion. The solute transport model indicates that the lateral spread of saline water towards inland is not occurring farther beyond a 2 to 5 km strip due to higher topographic elevations and the groundwater is following the topography. In the contaminated strip, the model predictions are made up to the year 2052 ,with respect to its vertical and lateral spread.
Key words: Solute transport modeling, Hydrogeochemical investigations, Polluted coastal aquifer, Inter stream region, Pennar and Upputeru Rivers.

Climatology of Tornadoes over northwest India and Pakistan; and Meteorological Analysis of recent Tornadoes over the Region

S.C. Bhan*1, Surender Paul2, Kalyan Chakravarthy1, Rahul Saxena1, Kamaljit Ray1 and Neetha K. Gopal1
1India Meteorological Department, Mausam Bhawan, Lodhi Road, New Delhi-110003
2Meteorological Centre, Sector-39A, Chandigarh-160038
*Corresponding Author:

Occurrence of tornadoes over northwest India and adjoining parts of Pakistan is not known to be as frequent as that over east India and Bangladesh. This study presents a climatological analysis of all the reported tornadoes in the region collected from diverse sources and analysis of meteorological conditions associated with some recent tornadoes. There have been reports of 15 tornadoes during last 110 years (1903-2012) in the region. Reports of 12 tornadoes in recent 36 years (1975 to 2010) make it one tornado every three years. The frequency of occurrence has been found to be about 1×10−6/yr/km2, which is one order lower than that reported for Bangladesh. The pre-monsoon season (March – June) has been found to be the most likely period of occurrence of these events over the region as two thirds of the tornadoes have occurred during this season. Half of the events (for which dates were available) have occurred during the month of March. Analysis of meteorological conditions shows that most of the tornadoes in the region were associated with an area of convergence of low level moist winds overlain by an area of upper level divergence provided either by a trough in middle and upper tropospheric westerlies to the west of the low level convergence. Total-Total Index, SWEAT Index and K-Index were found to be good indicators of the possibility of occurrence of severe thunderstorms/tornadoes over the region.
Key Words: Tornado, northwest India, Pakistan, climatology, pre-monsoon season, trough, convergence, westerlies, stability indices.

Intra-seasonal changes and long range forecast of rainfall during 2013 southwest monsoon season based on South Indian Ocean Convergence Zone model

Onkari Prasad*1, O.P. Singh2 and K. Prasad3 
1 43, Ritu Apartments, A-4 Paschim Vihar, New Delhi-110063
2 B44, First Floor, Parshvnath Paradise, Mohan Nagar, Distt: Ghaziabad-201007 (U.P.)
3 D-104, Seema Apartments, Block-7, Sector 11, Dwarka, New Delhi-110 085
*Corresponding Author :

Large intra-seasonal changes took place during 2013 southwest monsoon. An attempt had been made to capture the likely changes in rainfall scenario due to these intra-seasonal changes by issuing forecast updates. The forecast updates were able to capture the improvement in rainfall scenario during the first half of the season, i.e., June-July. However, reduction in rainfall during the second half of the season could not be captured in the forecast update issued in the first week of August. It has been shown, from an examination of weekly SST anomalies and the activity of South Indian Ocean Convergence Zone (SIOCZ) during the season that the availability of weekly forecast SST anomalies from the Indian Ocean region, at least one month in advance, is crucial to foreshadowing likely intra-seasonal changes in the activity of SIOCZ and thereby in rainfall scenario in forecast updates.
Key words: Southwest monsoon, long range forecast, South Indian Ocean Convergence Zone, intra-seasonal changes, forecast updates.

Seasonal Variation of Daily Total Column Ozone (TCO), Its Depletion and Formation Role on Surface Temperature and Rainfall Over Chennai, India

S.Goswami*1 and S.K.Midya2
1Department of Chemistry, Dinabandhu Mahavidyalaya, Bongaon,North-24 Parganas- 743235
2 Department of Atmospheric Science, University of Calcutta, 51/2 Hazra Road, Kolkata-700019
*Corresponding Author:

Various studies based on ground and satellite measurements have shown that overall ozone concentration is declining globally. The present manuscript contains results of study on the variation of total ozone concentration over Chennai, India during different seasons. It is concluded that the trend of ozone concentration during different seasons varies. After a critical analysis the following important results are obtained:
(i)The total ozone concentration increases during the pre-monsoon and winter periods; (ii) The Total Column Ozone (TCO) decreased during the monsoon and post-monsoon periods, throughout the extent of study; (iii) The rate of formation of ozone during monsoon is found to decrease in oscillatory manner, with the rise of surface temperature; (iv) The rate of depletion of ozone during monsoon is found to increase with the rise of surface temperature. However, a decreasing trend is noticed with the rise of surface temperature during post-monsoon period;(v) The overall ozone concentration over Chennai for the period of our study has shown slightly increasing trend;(vi) The variation of total rainfall with the rate of change of TCO (Total Column Ozone) is also presented for different seasons over Chennai and (v)Detailed chemical kinetics of ozone chemistry is presented along with possible explanation.
Keywords: Total Column Ozone (TCO), Gangetic West Bengal (GWB), Marine Boundary Layer (MBL), Monsoon, Pre-monsoon, Post-monsoon, Winter, Chemical Kinematics.

Geographical Analysis of Rainy Days Over West Coast Region And Islands of India

Manjunatha S. Tyalagadi*1, G Krishnakumar2 and Tongdi Jamir3
1Lecturer, Government Sardars’ PU College, Belgaum, Karnataka, India
2 Director, NDC, India Meteorological Department, Pune, Maharashtra, India
3Environmental Science Department, University of Pune, Pune
*Corresponding Author:

Climate change (CC), due to natural and manmade causes has received the attention of atmospheric scientists during the last four to five decades. As a part of such studies worldwide, efforts have been made to ascertain the impact due to CC on the characteristics and dynamics of Indian summer monsoon rainy days. A detailed analysis of data pertaining to rainy days over the West Coast Region (WCR) and islands of India has been necessitated to understand the impact of CC on the Southwest monsoon behavior.
In this study, non-parametric test using the linear regression and student t-test were used to determine the existence and magnitude of any statistically significant trend in the seasonal rainy days, rainfall and cloud amount. To study the temporal trend of meteorological parameters, 60 years (1951-2010) daily rainy days data was collected for 16 selected stations distributed over 5 different Meteorological Subdivisions (MS) of India. The analysis reveals that the number of rainy days shows a significant decreasing trend during the monsoon season. However, the monsoon monthly trend shows mixed behavior. The decrease in rainy days was probed by the frequency of cyclones (1951-2010).The result indicates that the cloud amount and cyclonic systems prevailing over the WCR show decreasing trend. Further, investigations on rainy days indicate significant increasing trend during the last decade (2000-2010) over majority of the stations.
Key words: Geographical analysis, Climate change, Cloud amount, Cyclonic systems, West Coast Region, Linear regression, Student t-test, Meteorological Subdivisions, Rainfall trends.

Trend analysis and extreme events of temperature during post monsoon and winter seasons over Varanasi, Uttar Pradesh, India

R. Bhatla*1, Swaleha Tabassum2 and A. Tripathi1
1Department of Geophysics, Banaras Hindu University, Varanasi, India.
2Department of Botany, Banaras Hindu University, Varanasi, India.
*Corresponding Author:

The cold wave can be described as a rapid fall in temperature that affects agriculture, industries, commerce and other social activities. The aim of the present study is to find out the inter-annual and intra-seasonal variability of temperature for the post monsoon and winter seasons. The frequency of cold wave and severe cold wave has also been studied for four decades from 1971-2010. Frequency of cold wave and severe cold wave days for the four decades for the month of January is the highest among all the months. The number of cold wave events was more during post monsoon season than winter season and opposite in the case of severe cold wave events.
Key Words: Extreme temperature,Cold wave, severe cold wave, trend analysis, decadal.

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