Contents
of October, 1998 - Vol. XIX No.4
CONTOURS TO IMAGES - PART II: AEROMAGNETIC IMAGE OF WESTERN PART
OF CUDDAPAH BASIN AND ADJOINING CRYSTALLINES- A CASE STUDY
V. Babu Rao, Y. Sreedhar Murthy and K. Govindarajan
ENGINEERING GEOPHYSICAL SURVEYS: AN INTEGRATED APPROACH FOR SITE
AND ROUTE SELECTION OF OFFSHORE OIL TERMINAL IN THE GULF OF KUTCH, A CASE
STUDY
Ranjit Rath, C.C. Babu and V.V. Reddy
SPECTRAL ANALYSIS OF GRAVITY ANOMALIES OF THE NORTH-WESTERN PART
OF BANGLADESH
Md. Babul Islam, Shaikh Enayetullah, Md. Syed Mostafizur Rahman and Md.
Rezwanul Islam
IDENTIFICATION OF ZONES OF CORROSIVE GROUNDWATER USING RESISTIVITY
METHOD
K.K. Sharma and S. Jayashree
Shalivahan, Bimalendu B. Bhattacharya and Mrinal K. Sen
SUBDUCTION IN THE INDO-BURMA REGION: RELATIONSHIP BETWEEN THE
WBZ ZONE AND THE P,T & B AXES
S.P. Satyabala
CONTOURS TO IMAGES - PART II: AEROMAGNETIC IMAGE OF WESTERN PART
OF CUDDAPAH BASIN AND ADJOINING CRYSTALLINES- A CASE STUDY
V. Babu Rao*, Y. Sreedhar Murthy** and K. Govindarajan***
*National Geophysical Research Institute,
Hyderabad - 500 007
**Dept. of Geophysics, Osmania University, Hyderabad - 500 007
***Association of Exploration Geophysicists, Hyderabad - 500 007
Abstract
Display of Geophysical data in general,
and aeromagnetic data in particular, in image form enhances the visual
perception by several orders of magnitude in comparison to the conventional
contour maps. The recent advances made in the fields of digital data and image
processing and display technologies have succeeded to bring out the full
potential of the aeromagnetic surveys as a mapping tool and as a pre-eminent
component of all the major exploration programs. Availability of geophysical
data set in an equi-spaced rectangular grid form is an essential pre-requisite
to utilize the advantages of the state-of-the-art technologies. Digitization of
the available Indian aeromagnetic data set is thus a priority towards this
goal.
Using the Auto Trace and Digitising
Methodology evolved by us the aeromagnetic data set over the Proterozoic
Cuddapah basin and the adjoining crystallines is taken up as an illustrative
case study and the magnetic images in grey-scale, in colour and as shaded
relief are presented and their advantages over the conventional contour maps
are outlined.
It is pointed out that this is first of
the NGRI aeromagnetic data set to be brought out in a user-friendly display
mode. The magnetic data is corrected for the International Geomagnetic
Reference Field (IGRF) in contrast to that of the aeromagnetic map published
earlier. The efficacy of the Shaded relief map in mineral exploration with
particular reference to Diamond exploration is illustrated.
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ENGINEERING GEOPHYSICAL
SURVEYS: AN INTEGRATED APPROACH FOR SITE AND ROUTE SELECTION OF OFFSHORE OIL
TERMINAL IN THE GULF OF KUTCH, A CASE STUDY.
Ranjit Rath, C.C. Babu and V.V. Reddy
Engineers India Limited, Emgineers India
Bhavan, 1, Bhikaiji Cama Place, New Delhi - 110066
Abstract
Offshore oil terminals are built in
strategic locations to facilitate the import of crude oil, which forms a major
share of the current demand in the present Indian Petroleum industry. Because
of its low installation and maintenance cost, high and easy cargo handling
capacity and minimum gestation period in comparison to the other inshore import
facilities, such as Port & harbor jetties, it does possess an edge over the
others. An offshore terminal could be a Single Point Mooring (SPM) or a Multi
Point Mooring(MPM) system depending on the required cargo expected to be
handled and the site conditions.
The present paper discusses various
facets and the associated pros and cons prior to the selection of a suitable
site for a proposed offshore oil terminal of Single Point Mooring type (SPM) in
the Gulf of Kutch and finalisation of the associated submarine pipeline route.
The design criteria and site selection of the SPM, prior to fabrication and
installation, were finalised by undertaking detailed engineering geophysical
surveys and oceanographic investigations in and around a proposed area. This
has helped in understanding the prevailing geological condition i.e. both
seabed and sub-seabed geology, oceanographic and environmental parameters.
Based on the data collected during the survey, the SPM location was finalised
at a water depth of 33.7m below Chart Datum, keeping in view the size and
draught requirement of the cargo to be handled. Further, a suitable submarine
pipeline route, from the SPM to the Land Fall Point(LFP) that would further
connect to the Crude Oil Tank farm on the shore, was also selected out of two
proposed alternatives. As these factors are site specific, no general guideline
is applicable and thus require an intrinsic approach, meticulous observation
and interpretation of the collected data by specialists for economical and
successful design, installation and operation of the system.
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SPECTRAL ANALYSIS OF GRAVITY ANOMALIES OF THE NORTH-WESTERN PART
OF BANGLADESH
Md. Babul Islam, Shaikh Enayetullah, Md. Syed Mostafizur Rahman
and Md. Rezwanul Islam
Dept. of Applied Physics and Electronics,
Rajshahi University, Rajshahi - 6205, Bangladesh
Abstract
The gravity anomalies of the
north-western part of Bangladesh have been analyzed for geophysical
interpretations. Various useful existing spectrum-based data processing and
interpretational techniques have been used. It is found from the spectral studies
that most of the signal powers are associated with the deep-seated structures.
The presence of two different ensembles of causative sources (shallow and deep)
has been detected and their average depths have been estimated. The estimated
depth of the deep-seated sources with an analytical interpretational approach
(Smith rule) is found to be in good agreement with the average depth of the
ensemble of the deep-seated sources with the spectral interpretational
technique. The estimated depths of the deep and shallow sources are also
compared with the available borehole, geological and geophysical
interpretations. The deep-seated sources are the intrabasement intrusives
producing the major regional gravity anomalies and the shallow sources are the
Pre-Cambrian basement rocks in the study area.
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IDENTIFICATION OF ZONES
OF CORROSIVE GROUNDWATER USING RESISTIVITY METHOD
K.K. Sharma and S. Jayashree
Department of Applied Geology, University of
Madras Guindy Campus, Madras - 600 025, India
Abstract
Increased demand for water have
stimulated development of underground water resources. The suitability of
groundwater for domestic, industrial and irrigational purposes is determined by
its quality. When groundwater is distributed through either iron pipes or
concrete pipes, the characteristics like corrosion and encrustation are to be
assessed in detail in order to protect the supply system.
In this paper, the importance of
resistivity methods in demarcating the zones of corrosive groundwater is
outlined. As a case study, zones of corrosive groundwater in the Vaigai basin
have been demarcated using resistivity method. This has been correlated with
the available geochemical data and it has been found that resistivity studies
can help in not only identifying the corrosive zones; but also in identifying
the formation that contributes to this corrosion and hence help in limiting the
depth of well drilling.
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INTERPRETATION OF SELF-POTENTIAL
ANOMALIES BY NONLINEAR INVERSION
Shalivahan*, Bimalendu B. Bhattacharya and Mrinal K. Sen
* Dept. of Applied Geophysics, Indian School
of Mines, Dhanbad - 826 004, India
** Institute for Geophysics, The University of Texas at Austin, 8701 N Expwy,
Austin TX 78759-8397 USA
Abstract
The method of nonlinear inversion by
Very Fast Simulated Annealing (VFSA) – a variant of Simulated Annealing (SA),
has been used to interpret self potential data, both synthetic and observed. The
model parameters are generated from a Cauchy-like distribution which enables a
fast cooling schedule. The VFSA requires a temperature for each model parameter
and the temperature to be used in the acceptance criterion may be different
from the model parameter temperature. The algorithm for VFSA has been developed
for simple targets like sphere, cylinder and sheet. The algorithm has been
first tested on theoretical models. Subsequently field data have been
considered for which the interpreted results by other methods are available for
comparison. The agreement between the results obtained by VFSA and other
methods is good.
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SUBDUCTION IN THE INDO-BURMA REGION: RELATIONSHIP BETWEEN THE WBZ
ZONE AND THE P,T & B AXES
S.P. Satyabala
National Geophysical Research Institute,
Hyderabad - 500 007
Abstract
The Indo-Burma region (longitude
92ºE-98ºE & latitude 20ºN-28ºN) is a subduction zone where the Indian plate
underthrusts the South-Eastern Asian plate. Harvard Centroid Moment Tensor
solutions of 65 earthquakes, which occurred in this region during 1977-1996,
are analyzed to examine the relationship of the T/B/P axes of the Moment Tensor
with the geometry of the surface of the Wadati-Benioff Zone (WBZ). The
earthquakes in this region have focal mechanisms of mixed type with a large
number of them having a predominant strike-slip or thrust components. This
study shows that the WBZ, defined by the eastward dipping inclined zone of
earthquakes up to 200 km depth under the Indo-Burman ranges, has a predominant
downdip tensional stress regime, which is typical of intermediate depth
seismicity of active subduction zones.
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