Current Issue

March, 2019   ||  Volume 23 No.2

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Delineation and sustainable development of groundwater resources in granitic terrain using electrical resistivity tomography

S.N. Rai* and S. Thiagarajan
CSIR-National Geophysical Research Institute, Hyderabad-500007, India
*Corresponding author: snrai_ngri@yahoo.co.in

ABSTRACT
Hard rock’s possess negligible primary porosity but due to inherent secondary porosity in the form of geological structures such as faults, fractures, joints etc, these rocks are rendered permeable to allow movement and storage of groundwater in limited quantity. Because of sporadic distribution of these water bearing geological structures, their delineation is a challenging task. Groundwater saturated geological formations/ structures are characterized with appreciably lower resistivity in comparison to those devoid of groundwater. Because of this, resistivity method is found to be most suitable among all the geophysical methods in delineation of groundwater bearing zones in all types of geological formations in general and hard rock terrains in particular. This paper discusses the efficacy of 2D Electrical Resistivity Tomography (ERT) to delineate groundwater bearing zones in complex hydrogeological environs like granitic terrains with the help of case studies from sites located in and around Hyderabad (Telangana state, India). ERT results have also been used to identify suitable sites for managing recharge of groundwater resources. This study has helped in establishing some criterion about the possibility of occurrence of potential groundwater resources in similar geological environs.



Geophysical investigation for copper and gold mineralization around Dhani-Basri and Todi ka Bas area, Dausa and Alwar districts, Rajasthan

D.C. Naskar*1, and A.V. Kulkarni2
1Southern Region, Geological Survey of India, Bandlaguda, Hyderabad-500068
2Central Region, Geological Survey of India, Seminary Hills, Nagpur-440006
*Corresponding author: dcnaskar@yahoo.com

ABSTRACT
Rocks exposed in the study area, have indicated presence of isolated outcrops of quartz-sericite mica schist, amphibolite, quartzite and metasedimentary, within the Banded Gneissic Complex (BGC)/Mangalwar complex that host a number of lead, zinc and copper deposits. Today, there is a challenge before geoscientists, to discover new mineral deposits, by an exploration technique, which have low risk, consumes less time and also cost effective. Accordingly, geophysical surveys comprising SP, magnetic, IP (TD) cum resistivity, gravity and resistivity sounding have been carried out in Dhani-Basri and Todi ka Bas area, Dausa and Alwar districts of, Rajasthan, for locating base metal occurrences. IP survey has delineated several anomaly zones, where strike length varies from 400 m to 1500 m. Chargeability values of zone-I, zone-II and zone-III, are ranging from 16-22 mV/V. Zone-I supported with low SP value -100 to -200 mV, corroborate well with the Dhani-Basri known deposit. Chargeability values of zone-IV, zone-V, zone-VI and zone-VII, range from 15-24 mV/V, while peak chargeability value of zone-V is observed as 30 mV/V, over a background value of 10 mV/V. Chargeability cum resistivity pseudo-section have shown depth persistence of the inferred conductors based on the contour pattern. These chargeability zones are associated with low SP, low resistivity and moderate magnetic responses. Further, Bouguer anomaly profiles reflect a region where borehole intersected a mineralized zone. Bouguer anomaly contour map indicates a fault zone, depending on the trend of the contour that corroborate well with the regional schistosity. Gravity high closure has been observed mainly for metamorphic content below the alluvium cover. The interpreted layers by Schlumberger resistivity sounding are top soil, hard rock/fractured granite-gneiss and the Archaean basement. The SP, magnetic and gravity data have also picked up structural/lithological trend quite well. However, to strengthen the survey results, the resistivity map is compared with chargeability map; those who have intersection area between low resistivity and high chargeability (> 24 mV/V) are considered the prospective zones for base metal mineralization. Further, the mineralization is structurally controlled by a shear zone, and sulphide (chalcopyrite, pyrrhotite and pyrite) with gold are hosted in the silicified zone.
Keywords: Dhani-Basri area, Copper-gold mineralization, Integrated geophysical surveys, Hard rock/fractured granite-gneiss, Structural/lithological trend.



A MATLAB Based Code for gravity data Corrections

K. Satish kumar1, Debraj Midya2, M. Tirupathi1*, and R.K. Tiwari1
1CSIR-National Geophysical Research Institute, Hyderabad-500007, Telangana, India
2Indian Institute of Technology Bombay, Mumbai, India
* Corresponding author: mtirupathi@gmail.com

ABSTRACT
An interactive MATLAB based code, designed for processing of relative ground gravity data. This interactive CODE is robust to compute Bouguer anomalies from relative land gravity data, acquired with reference to single standard absolute gravity base. The processed data will be viewed in the form of excel spreadsheet and graphical window. The efficacy of the CODE is tested on the real data set near Umred Coal field, Maharashtra and found to be feasible for handling gravity data sets for precise interpretation of the results. 1D spectral analysis of the Bouguer anomaly data shows that the depth to the basement varies from 0.5 km to 1.3 km over which Gondwana group of rocks are emplaced. Similarly, thickness of the trap is found to vary from 0.25 km to 0.6 km. The obtained results are in good agreement with the previous gravity and Magnetotelluric studies.
Keywords: MATLAB; Gravity; Bouguer anomalies; Gondwana; 1D Spectral Analysis.



Rapid Visual Screening of RC frame buildings in 2001 Bhuj earthquake affected Rambaug area of Ahmedabad, Gujarat

Russi Modi* and Kapil Mohan
Institute of Seismological Research, Next to Petroleum University, Raisan-382007, Gandhinagar, Gujarat.
*Corresponding author: modirussi017@gmail.com  

ABSTRACT
The buildings in Ahmedabad experienced heavy damage in the 2001 Bhuj earthquake, which exposed the deficiencies in their design and construction practices. The enhanced seismicity in the region warrants assessment of seismic vulnerability to aid engineers in urban development. The current study attempts to assess the vulnerability of RC frame buildings using Rapid Visual Screening (RVS) in the Rambaug area (Ahmedabad) where the collapses of a similar type of buildings were observed due to 2001 Bhuj earthquake. The RVS of 100 RC frame buildings was conducted. The performance score of the surveyed building ranges from 20 to 125. The parameters such as soft storey and overhang are found in most of the surveyed buildings, which make the buildings vulnerable to earthquake. The vulnerability here is defined as a relative measure based on the obtained performance score of the considered buildings. Most of the buildings lay in the performance score range of 43-84, which indicates moderate vulnerability of these buildings due to earthquake occurrence.
Keywords: Earthquake, Vulnerability assessment, Rapid visual screening.



Onset of southwest monsoon- A study of the precursors in South Indian Ocean
 

Onkari Prasad1*, K. Prasad2 and O. P. Singh3
143, Ritu Apartments, A-4 Paschim Vihar, New Delhi-110063
2D-104, Seema Apartments, Sector 11, Dwarka, New Delhi-110085
3B44, First Floor, Parshvnath Paradise, Mohan Nagar, Ghaziabad (U.P.)-201007
*Corresponding author: prasadonkari123@yahoo.in

ABSTRACT
Satellite observed cloud data from the Indian Ocean region are now available for more than 50 years. An analysis of the cloud data for a period of 16 years (1972-1989 except 1978 and 1981), had shown that precursors to monsoon develop as different features in the activity of South Indian Ocean Convergence Zone (SIOCZ) (Eq.-20ºS and 40-100ºE). This had formed the basis for proposing SIOCZ model of long range forecast of rainfall over India, during the southwest monsoon period. Cloud data from 1990 onwards were used for preparing forecast on the real time basis and to further improve the model. The model has since produced reasonably good forecast of monsoon rainfall for India as a whole and also for individual meteorological subdivisions (numbering 36) for a period of 29 years (1990-2018), and in the districts of Tamilnadu for 14 years (2005-18), Himachal Pradesh for 11 years (2008-18), Andhra Pradesh and Telanagana for 4 years (2015-18) and Maharashtra and Goa for 3 years (2016-18). This has confirmed close relationship between the precursors as identified in cloud data, and the activity of southwest monsoon over India. In some of the years, the precursor did change during the season. Change in the rainfall scenario, resulting due to the change in the precursor, is included in the forecast update/updates. The relationship between precursors and onset of monsoon over Kerala has been further studied using satellite observed cloud data for a period of 50 years (1969-2018). It has been shown that (i) onset of monsoon over Kerala is related to the development of precursor, as a feature in the activity of SIOCZ, (ii) there is no one to one relationship between the date of onset and the performance of monsoon, and (iii) a close relationship between the precursors and the activity of monsoon during the season, has resulted in providing a reliable information on the performance of monsoon.
Key words: Southwest monsoon, Satellite observed cloud data, South Indian Ocean Convergence Zone, Rainfall.



A case study on pre- and post-monsoon seabed topography using bathymetry near Kalingapatnam, Srikakulam District, Andhra Pradesh (India)

S. Balasingh John Samuel1*, Y.Srinivas1, and R. Subramanian2
1Centre for GeoTechnology, Manonmaniam Sundaranar University, Tirunelveli-627012, India
2 Institute of Remote Sensing, Anna University, Guindy Campus, Chennai-600025, India
*Corresponding author: geophysingh@gmail.com

ABSTRACT
A study of seabed topography is important to understand the landforms under sea water, which has various oceanographic applications like navigation safety, nautical charts, water volume computation, seabed sediment computation, pollution control, sediment transport, under water engineering, harbour and docks construction etc. Bathymetry is one of the tools to delineate seabed topography using echo sounding principle. In this study, bathymetric survey was carried out at near-shore areas by covering about 10 km distance along the coast and into the sea up to 20 m contour at 100 m line spacing, during pre- and post-monsoon seasons. The survey area was spitted into three zones and data was collected using dual frequency echo-sounder, which was processed and presented in Chart Datum, based on tides measured at every 10 minutes interval during survey period, using vale-port tide gauge at river Vamsadhara. The results demonstrate that the water depth is increasing gradually towards seaward and structuring gentle slope from seashore. The depth contours are running parallel to the coast during both seasons. The seabed profiles show that the seabed experienced erosion and deposition at river mouth and also in the northern side of study area. The overall seabed topography suggests that this region is suitable for coastal development activities in the southern part, where the seabed has adequate natural depth and lesser sediment migration.
Key Words: Pre- and post- monsoon bathymetry, Sediment deposition, Sediment volume computation, Near-shore sediment deposition, Monsoon, Kalingapatnam.


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Assessment of land degradation and desertification due to migration of sand and sand dunes in Beluguppa Mandal of Anantapur district (AP, India), using remote sensing and GIS techniques

B. Pradeep Kumar, K. Raghu Babu*, M. Rajasekhar and M. Ramachandra
Department of Geology, Yogi Vemana University, Kadapa, Andhra Pradesh, India.
*Corresponding author: dr.kraghu@gmail.com

ABSTRACT
Land degradation and desertification by means of sand migration, is one of the major problems facing the world today. Degradation is the process of conversion of productive land into waste land or degraded to desertified land. Degradation is influenced by the natural and anthropological causes in arid and semi-arid regions. According to a report by the Indian Space Research Organization (ISRO), 96 million hectors or 30 percent of India’s agricultural land, is affected by the land degradation. The present study deals with identification, mapping and assessment of desertified areas in Beluguppa Mandal of Anantapur district, using geospatial techniques, aided by Landsat satellite images. The main reason for land degradation and desertification of this area is the migration of sand and sand dunes by aeolian process. Present study is focused to define the desertification in the study area during 18 years period beginning 2000 and onwards. Hence, temporal data of Landsat satellite image of past 18 years (i.e., 2000-2018), were collected and processed, to know how much of land is covered by migrated sand dunes and get desertified. By using geospatial technologies like satellite remote sensing (RS) and geographical information system (GIS), identification and mapping of desertified areas and progress of desertification were made in the present study. The results of the present study clearly reveal that 26 hectares of agriculture land is desertified in Srirangapuram village, and an area of 14 hectares of agriculture land is desertified in Narinjagundlapalle village in Beluguppa mandal of Anantapur district, A.P.
Key Words: Desertification, waste land, Semi-Arid, Landsat, Geospatial techniques, Anantapur district.


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SHEAR ZONES: A Tutorial
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T.R.K. Chetty 
CSIR- National Geophysical Research Institute, Hyderabad – 500 007
E.mail: trkchetty@gmail.com


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