IJMS 43(3) 337-339

Indian Journal of Marine Sciences
Vol. 43 (3), March 2014, pp. 337-339
High resolution satellite gravity over a part of the Sir Creek offshore on west
northwest margin of the Indian subcontinent
T J Majumdar*1 & R Bhattacharyya2
1
Space Applications Centre (ISRO), Ahmedabad – 380 015, India
Centre of Excellence for Energy Studies Oil India Limited, Guwahati - 781 022, India
*[E-mail: [email protected]]
2
Received 6 August 2012; revised 12 November 2012
Satellite altimetry has been used to delineate subsurface geological structures analogous to gravity anomaly maps
generated through ship-borne survey. In this study, free-air gravity image has been generated over the Sir Creek offshore
region on west northwest margin of the Indian subcontinent, using very high resolution data base as generated from Geosat
GM, ERS-1, Seasat and TOPEX/POSEIDON altimeter data and ETOPO -1 (1’ resolution) bathymetry data superimposed
over the gravity data. The high resolution gravity data has been found most suitable for exploration in the offshore region
and for lithospheric studies. Moreover, continental shelf and slope regions could be identified alongwith bathymetry data.
[Keywords: Satellite altimetry, GEOSAT geodetic mission, Sir creek offshore, Free-air gravity, ETOPO-1 bathymetry]
Introduction
Satellite altimetry offers to act as an inexpensive
and rapid reconnaissance tool for the sparsely
surveyed Indian Ocean region. It can as well be used
to delineate subsurface geological structures as
observed on the gravity anomaly maps generated
through ship-borne survey1. Presently available dense
satellite altimeter data with ~ 4 km off-track
resolution makes a detail recovery of the marine
gravity field which can be used for more detailed
geological exploration of the sea floor. With the
advent of high resolution altimeters like GEOSAT Geodetic Mission (GM) it has now become possible
to obtain more details for the offshore exploration.
With compilation of multiple radar altimeters e.g.
ERS-1/2, GEOSAT GM, TOPEX/POSIEDON and
Seasat, the high resolution data could be generated,
which gives more valuable information of the offshore
region. A number of known megastructures e.g.
Bombay High, Saurashtra platform, Carlsberg ridge,
85oE ridge, Ninetyeast ridge, etc. could be precisely
identified and successfully interpreted with the help of
such high resolution altimeter data over the Indian
offshore region1. Some of the anomalous zones
(basins near Mangalore and off Bombay High in the
western offshore and Krishna-Godavari basin, Palar
basin off Madras coast in the eastern offshore) have
been identified as potential sites for occurrences of
hydrocarbon-bearing structures2. The Carlsberg ridge,
the Bombay High region in the western Indian
offshore could be more precisely identified using high
resolution satellite gravity data which has helped to
delineate the detailed transform faults and fracture
zones in this region2,3.
Sir Creek is a 96 km strip of water between India
and Pakistan in the Rann of Kutch marshland. The
creek, which opens up into the Arabian Sea, divides
the Kutch region of Gujarat, India with the
Sindh province of Pakistan. It is located at
approximately 23°58′N, 68°48′E. The deepest
navigable line in the Sir Creek is the Indian boundary
which generally runs along the middle of the Creek7.
Sir Creek and its surrounding region has not been
sufficiently explored using satellite geoid/gravity
data. Satellite altimetry has recently emerged as an
efficient alternative for expensive and hazardous shipborne gravity survey2,3. Averaged Sea Surface Height
as obtained from satellite altimeter is a good
approximation to the classical geoid, which contains
information regarding mass distribution in the entire
earth. Anomalies (highs and lows) in geoidal
surface have been directly interpreted in terms of
subsurface geological features e.g. transform faults,
basement highs and lows etc4. Geoidal anomalies
are also converted to free-air gravity (FAG) anomalies
which are particularly useful in the deep sea where
traditional ship-borne geophysical data are either
unavailable or scanty. Rapp5 has developed a method
338
INDIAN J MAR SCI , VOL . 43 , NO.3, MARCH 2014
for the prediction of gravity anomaly using spherical
harmonic coefficients up to degree and order 30
and above. Sandwell and Mc Adoo6 have generated
gravity field of the Southern Ocean and the Antarctic
Margins from Geosat data. Majumdar et al.1,4,
have developed a brief methodology for offshore
structure
delineation
using
altimeter
data.
Fig. 1 shows the generalized data processing steps for
deriving marine gravity and geoid from satellite
altimetry data.
obtained from Geosat GM (Geodetic Mission),
ERS-1, TOPEX/POSEIDON, and Seasat altimeter
data8 over the Sir Creek region. Because of
being high density in nature (off-track
resolution~3.33 km), sea surface parameters as
well as gravity derived from these data are more
reliable and detailed. Details of the methodology
for obtaining high resolution geoid and gravity
from altimeter-derived sea surface height have
been discussed elsewhere1,8 .
Materials and Methods
Study area of the Sir Creek offshore, with
latitude and longitude limits of 23-25 o N and
65-71 o E respectively, has been used to
generate the satellite-derived gravity anomaly
data for proper geological interpretation of
regional features.
Results and Discussion
Fig. 2 shows the high resolution free-air gravity
image over the Sir Creek and its surroundings.
Generated FAG over the region varies between 126 to 66 mGal approximately. ETOPO-1
(1 minute) bathymetry contours of 200 m and 2000
m have been superimposed over the high resolution
gravity anomaly data. Geological features including
the continental shelf, the slope region, the Swatch
region on the left (knows as the Indus Canyon,
as well), the Indus Delta etc. could be sharply
delineated using high resolution gravity data. The
continental shelf region has also been marked in
Fig. 2. The continental slope ends at 2000 m depth.
We have shown the 2000 m isobath for the same
which actually runs almost parallel to 200 m
isobath but turns below the figured area. Hence it
could not be shown in full.
Generation of high resolution database
Hwang et al.8 have done a very detailed data
assimilation using various altimeter data sets and
Levitus topography for calculation of the
deflection of the vertical and then generating 2 × 2
minutes (4 × 4 km) grid. Free-air gravity image
has been generated using high density data base
Fig. 1—Generalized data processing steps for deriving marine
geoid and gravity
As can be observed from Fig. 2, a no. of rivers
from the Indus basin has confluenced with the
Arabian sea and hence a good amount of sediment
deposit had taken place9. The shelf of the Indus
delta remains largely unstudied. Its most prominent
feature is the Indus Canyon or ‘‘The Swatch’’, a
relic feature of the pre-Holocene relief (Fig. 2),
which dissects the shelf to within 20 m water depth
at 3.5 km offshore of the Indus delta9. A no. of
gravity lows could be delineated in this region
which may be further explored for potential
hydrocarbon-bearing structures in this region.
A few gravity highs could also be located with
probable basement highs. Major lineament trends
observed in the study area are NW-SE, NNW-SSE
and NE-SW. This may give some information
related to the rotation of the Indian
plate towards NW-SE as well as the existing
neotectonic movements in the region. No reliable
single-survey bathymetric data were available for
the coast east of the Sir Creek9.
MAJUMDAR & BHATTACHARYYA: HIGH RESOLUTION SATELLITE GRAVITY
339
Fig. 2—High resolution free-air gravity image over the Sir Creek and its surroundings (ETOPO-1 bathymetry contours 200 m and 2000
m are superimposed over gravity anomaly)
Conclusions
Gravity image generated from high resolution data
has been found useful for delineation of the
various structures and geological/geomorphological
features, some of which may be prospective for
hydrocarbon exploration in this region10,11. Moreover,
continental shelf and slope regions could be identified
alongwith bathymetry data. In the western offshore,
the major trends found are NW-SE, NNW-SSE and
E-W as observed earlier12. Major trends observed in
this study are NW-SE, NNW-SSE and NE-SW.
From the above, it is concluded that high resolution
satellite-derived free-air gravity map is a useful
tool for subsurface mapping and exploration of the
ocean basins.
For the prevailing security restrictions, lat./lon.
coordinates have been omitted in the image.
Acknowledgements
Authors are thankful to Prof. C. Hwang, National
Chiao Tung University, Taiwan for his help in data and
the related software. They are also thankful to Shri A.
S. Kiran Kumar, Director, SAC for his keen interest in
this study. TJM wishes to thank CSIR, New Delhi for
Emeritus Scientist Fellowship since January, 2011.
References
1
Majumdar T J & Bhattacharyya R, An Atlas of very high
resolution satellite geoid/gravity over the Indian offshore,
SAC Tech. Note No. SAC/RESIPA/MWRG/ESHD/TR21/2004 (Space Applications Centre, Ahmedabad, India) 2004.
2
Chatterjee S, Bhattacharyya R, Michael L, Krishna K S &
Majumdar T J, Validation of ERS-1 and high resolution
satellite gravity with in-situ ship-borne gravity over the
Indian offshore regions – accuracies and implication to
subsurface modeling, Mar Geodesy, 30 (2007) 197-216.
3
Chatterjee S, Bhattacharyya R & Majumdar T J, Utilization
of high resolution satellite gravity over the Carlsberg ridge,
Mar Geophys Res, 28 (2007) 309-317.
4
Majumdar T J, Mohanty K K, Mishra D C & Arora K,
Gravity image generation over the Indian subcontinent using
NGRI/EGM96 and ERS-1 altimeter data, Curr Sci, 80 (2001)
542–554.
5
Rapp R H, The determination of geoid undulations and
gravity anomalies from Seasat altimeter data, J Geophys Res,
88, C3 (1983) 1552-1562.
6
Sandwell D T & Mc Adoo D C, Marine gravity of southern
Indian oceans and Antarctic Margins from Geosat, J Geophys
Res, 93 (1988) 10389-10396.
7
Sir
Creek
Wikipedia,
the
free
encyclopaedia.
en.wikipedia.org/wiki/Sir_Creek
8
Hwang C, Hsu H Y & Jang R J, Global mean surface and
marine gravity anomaly from multi-satellite altimetry:
application of deflection-geoid and inverse Vening Meinesz
formulae, J Geodesy, 76 (2002) 407-418.
9
Giosan L, et al., Recent morphodynamics of the Indus delta
shore and shelf, Continental Shelf Res, 26 (2006) 1668–1684.
10 Bhattacharyya R, Verma P K & Majumdar T J, Study of high
resolution satellite geoids/gravity data over the western
Indian offshore region for tectonics and hydrocarbon
exploration, Ind J Mar Sci, 38 (2009) 116-125.
11 Biswas S K, Rift basins in western margin of India and their
hydrocarbon prospects with special reference to Kutch Basin,
Amer Assoc Petr Geol Bull (AAPG), 66 (1982) 1497-1513.
12 Majumdar T J & Bhattacharyya R, A comparative evaluation
of the gravity signatures over a part of the western Indian
offshore for lithospheric studies, Ind J Geo-Mar Sci, 40(4)
(2011) 491-496.

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