Current Issue

September, 2016   ||  Volume 20 No.5

Editorial


1
Efficacy of anisotropic properties in groundwater exploration from geoelectric sounding over trap covered terrain

G. Shailaja1, M. Laxminarayana1, J.D. Patil2, V.C. Erram1, R.A. Suryawanshi3 and Gautam Gupta*1
1Indian Institute of Geomagnetism, New Panvel (W), Navi Mumbai 410218, India
2D.Y. Patil College of Engineering & Technology, Kasaba Bawada, Kolhapur 416006, India
3Yashwantrao Chavan College of Science, Karad-Masur Road, Karad 415124, India
*Corresponding Author: gupta_gautam1966@yahoo.co.in

 ABSTRACT
Electrical resistivity study assumes a special significance for mapping aquifer in hard rock area and is also widely used in delineating the lateral and vertical distribution of sub-surface. 23 Vertical electrical soundings (VES) with Wenner electrode configuration were carried out over Chikotra basin, located in the southern part of Kolhapur district in the Deccan Volcanic Province (DVP) of Maharashtra to delineate the groundwater potential zones and anisotropic properties of fractures for sustainable groundwater development within the study area. The results illustrate that the secondary geophysical indices provide a constructive solution in delineating the fresh water aquifers in the trap covered area. The longitudinal conductance (S) value vary from 0.016 to 5.44 Ω-1, suggesting that the entire study area reveals good to weak aquifer protective capacity rating. The low value of the protective capacity in the northern and central part of the basin is due to the absence of significant amount of clay as an overburden impermeable material, thereby enhancing the percolation of contaminants into the aquifer. The large variation in the coefficient of anisotropy from 1 to 6.18 at the 23 VES data sites, suggests the anisotropic disposition of the aquifers in basaltic region. The fracture porosity inferred from the geophysical parameters and specific conductance of groundwater varies from 0.0001% to 0.556% in the study area, signifying different degrees of water saturation within the basaltic layers. The high-porosity zones corroborate with the high anisotropy values, indicating significant reserves of exploitable groundwater. This practice of analyzing VES data provided the direct solution to resolve problems in different hard rock terrains with a severe scarcity of groundwater, which has a great social impact. 
Key words: Electrical resistivity, Chikotra basin, anisotropy, porosity, groundwater, Deccan Volcanic Province.



Longitudinal inequalities in Sq current system along 200 - 2100 E meridian

S. K. Bhardwaj* and P. B. V. Subba Rao
Indian Institute of Geomagnetism, New Panvel, Navi Mumbai 410 218 India
*Corresponding Author: sandeep@iigs.iigm.res.in

ABSTRACT

In the present study, longitudinal inequalities in Sq current system have been examined utilizing the data of northern and southern hemispheric stations for the period 1976 - 1977 along 200-2100 E meridian. The anomalous behavior in the horizontal component (H) at a few southern hemispheric stations reveal that the solar quiet daily (Sq) variations in longitudinal sector (20o-120o E) do not show the expected V type or inverted V shaped variations but instead are marked by northern hemispheric D variations.
The technique of Principal Component Analysis (PCA) is applied to the D, H and Z components of the Earth’s magnetic field. First Principal Component (PC-1) brings out a well defined anticlockwise loop with focus near geomagnetic latitude (~ 26.0o N) at 11 hours local time in the northern hemisphere and clockwise with focus near geomagnetic latitude (~ 43.2o S) at 12 hours local time in the southern hemisphere. This phenomenon has been observed during summer months and disappearance of the northern and southern hemispheric ‘Sq-Vortex’ during winter months. Anomalous deformation of Sq vortex, confined to longitudinal sector (20o to 120o E) may arise due to the changes in the local ionospheric conductivity and tidal winds driven by the main geomagnetic field.
Key words: D, H and Z components of Earth’s magnetic field, Principle component analysis, Sq current system, Sq vortex deformation.



Time-lapse seismic response evaluation based on well log data for Ankleshwar reservoir, Cambay basin, India

U.Vadapalli* and N.Vedanti
CSIR – National Geophysical Research Institute, Hyderabad-500007, India
*Corresponding Author: umageo.anm4@gmail.com

ABSTRACT
Time-lapse seismic reservoir monitoring can image fluid-flow effects in a reservoir if the changes in seismic properties of the reservoir due to production or on-going recovery processes are large enough to detect. Thus, before acquiring a time-lapse seismic data, it is necessary to carry out feasibility study for time-lapse seismic reservoir monitoring to get an estimated seismic response. In the present study, Gassmann fluid substitution analysis and forward modeling based on well logs have been carried out to predict the seismic response of a paysand of Ankleshwar reservoir, which is being studied for CO2 – EOR. In this reservoir for enhanced oil recovery (EOR), CO2 injection into a paysand of the reservoir is found to be appropriate, taking into cognizance its success in different reservoirs all over the world.
The seismic response of paysand S5 in a well is modelled for different saturations and a variable thickness of CO2 in the paysand. It is observed that because of the first appearance of CO2, sudden drop in acoustic impedance of the paysand would lead to detectable time shift at the top. However, as CO2 occupies full thickness of the paysand time shift at the top is reduced. Time shift at the bottom responds to overall velocity drop in full thickness of the paysand and it could not be detectable. We also inferred that in this case time-lapse time shift analysis would be more helpful compared to the amplitude analysis and it should be possible to image CO2 plume in the reservoir. The replacement of oil and water in the paysand with CO2 might lead to 9% drop in P-wave velocity.
Key words: Time-lapse seismic response, Gassmann’s equation, fluid replacement modeling, well log data, CO2 injection, CO2 – EOR, Ankleshwar reservoir.


Assessing Quality of Masonry Dam using Seismic and Electrical Tomography 

M.S. Chaudhari*, M. Majumder, V. Bagade and S. Ranga
Central Water and Power Research Station, Pune-411024, Maharashtra, India
*Corresponding Author: geophysics.cwprs@gmail.com 

ABSTRACT
The ageing and degradation of dam structures is an inevitable problem and its consequences on the safety of the structure are important. Presently, site characterization using geotechnical engineering has some limitations to adequately describe the subsurface ground conditions. All geotechnical tests provide information from point to point and the values are interpolated in between places. These tests grossly under sample the subsurface and are frequently inadequate. Geophysical methods are useful as non-destructive tools that can provide information over large volumes as compared to point measurements. The use of seismic tomography and electrical resistivity imaging in the assessment of dam structure is very apt and useful. Seismic tomography survey was carried out in five horizontal and two vertical planes in the body of the Manikdoh masonry dam and one electrical resistivity imaging profile was taken on the top of the dam. The travel time data for tomography analysis was collected by placing geophones on the downstream face and hammer points on the upstream face of the dam. The compressional (P-) wave velocity distribution between each consecutive pair of source line and receiver line of the plane was computed using Simultaneous Iterative Reconstruction Technique. The weak zones, if present, reveal low P- wave velocity values and hence can be delineated. The reliability of travel time data is ensured by comparing the P- wave velocities at the point of intersection of common source to receiver pairs in horizontal and vertical planes. The tomography survey results revealed that the low velocity zones (velocity ranging between 1500 m/s to 2500 m/s) are between elevations 695 m to 705 m from chainage 463 m to 469 m. The four weak zones obtained from the horizontal planes matched well with that in vertical tomograms. Further, these low velocity zones are supported by presence of low resistivity patch (resistivity ranging between 129 Ω m to 829 Ω m) between elevation from 697 m to 693 m from chainage 462 m to 474 m in electrical resistivity imaging section.
Key words: Seismic tomography, dam safety, masonry dam, Imaging.



Chaotic nature of total column ozone over tropical station by time series analysis

P.Indira*1 and S. Stephen Rajkumar Inbanathan2
1 The Research and Development Centre, Bharathiar University, Coimbatore, Tamilnadu, India
2Postgraduate Research Department, The American College, Madurai-625 002, India
*Corresponding Author: indiraindhu2006@gmail.com

ABSTRACT
The paper deals with monthly total column ozone concentration over Kodaikanal, Tamilnadu. The basic rationale is to investigate the existence of chaos within the relevant time series. Method of measuring trend, Mann Kendall trend analysis, measuring self similarity, Lyapunov exponent is adopted here as the preferred research methodology. After a rigorous investigation, a low dimensional chaos with the persistent behaviour is identified within the time series pertaining to monthly total column ozone concentration over Kodaikanal, Tamilnadu.
Key words: Trend, Ozone, Tropical station, Time Series Analysis, Mann Kendall trend analysis, self similarity, Lyapunov exponent, chaos.



In and Around the Hazara-Kashmir Syntaxis: a Seismotectonic and Seismic Hazard perspective 

Hamid Sana and Sankar Kumar Nath*
Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur, India
*Corresponding Author: nath@gg.iitkgp.ernet.in

ABSTRACT
This study presents the seismotectonics of the Hazara-Kashmir Syntaxis and the surroundings. The detailed description of the origin, geology and structures of the Hazara-Kashmir Syntaxis is presented. The structural alignment of the Hazara-Kashmir Syntaxis is explained to be resulted by the shift in the motion pattern of the Indian plate from translational to translational-cum-rotational with the shift of the main boundary front from Main Mantle Thrust to Main Boundary Thrust. The crustal shortening in between the two limbs of the Hazara-Kashmir Syntaxis is accommodated by the out-of-sequence faults like the reverse Balakot-Bagh fault. The occurrence of the recent 8 October 2005 Kashmir Earthquake of Mw 7.6 has shown that these out-of-sequence faults are capable of triggering disastrous earthquakes. The same tectonic setup is observed in the northwestern part of the Kashmir Valley, a dominantly thrust type lineament named Drangbal-Laridora Fault, which is identified and delineated by characteristic morphotectonic indicators. A detailed seismicity analysis of the catalogue from 1937-2012 is also presented. The seismicity in the region is dominantly shallow (0-35 km) with a b-value of 0.88, which infers a high stress regime. Three methods are adopted to estimate the Maximum Credible Earthquake for the terrain, the probabilistic estimate based on earthquake catalogue, fault parameter approach and the convergence rates from GPS measurements. The Maximum Credible Earthquake estimated by the above discussed methodologies is Mw 8.1, Mw 7.7 and Mw 8.4 respectively. These estimates speak about the seismic hazard vulnerability of the region and demand a detailed seismic hazard assessment of the region.
Key words: Hazara-KashmirSyntaxis, morphotectonics, seismic hazard, seismicity analysis, maximum credible earthquake.


7

Insight into the tectonic and crustal understanding of lesser Himalayas along Purnea-Sevoke transect through geophysical studies 

D.C. Naskar*1, L.K. Das2 and M.K. Rai3
1 ER, GSI, Kolkata
2 Retd. Dy.D.G. (Geophysics), GSI, Kolkata
3 NR, GSI, Lucknow
*Correspoinding Author: dcnaskar@yahoo.com

ABSTRACT
Geophysical investigation employing deep electrical resistivity, gravity and magnetic techniques was carried out along Purnea-Sevoke (NH-31) road. The basement depth varies from 2917-4450 m, indicating huge relief. Three basement faults have been mapped over the transect. The Siwalik floor is quite undulatory in this part of the frontal fore deep region of the Himalayas.
The gravity profile along NH-31 from Purnea to Sevoke brought out two basin structures with upliftment of basement at km st 460 and km st 490. Spectral analysis of the said gravity profile brought out the Conrad discontinuity and the basement depth at 18.4 and 3.2 km respectively. 2D gravity modeling along the above transect indicates gradual deepening of basement towards the NE in addition to the features stated above. This is due to sagging of the crustal block at the foot hill region of Himalaya.
The magnetic anomaly between km st 465 to km st 500 is of fairly high order (400-1000 nT) in the area which supports the findings from the gravity survey. These are primarily due to upwarpment of basement in these areas. However presence of traps below the sediment cover is an added probability.
Key words: Lesser Himalaya, Bouguer anomaly, 2D modeling.


8

-An Opinion
Is Micro irrigation viable in helping small and marginal farmers? -need for an in depth scientific study 

P.R.Reddy
Director Grade Scientist ( Retd ), CSIR-NGRI, Hyderabad, 500 007.
Email: parvatarreddy@gmail.com

ABSTRACT
Micro irrigation is considered the best irrigation technique, especially in water stressed arid and semi arid tracts. However, there are some impediments to make it a viable irrigation practice, due to some practical problems encountered by economically backward small and marginal farmers. In this write up an effort has been made to analyse various facets of micro irrigation.


9
Reminiscences of a Field Geophysicist of Geological Survey of India 

I.C. Madhusudan
Director Geophysics, selection grade (Retd, GSI)


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