United Nations Convention on Law of the Sea (UNCLOS) defines the continental shelf to comprise of the seabed and subsoil of the submarine areas of a coastal State that extend beyond its territorial sea throughout the natural prolongation of its land territory to the outer edge of the continental margin (comprising the geological shelf, slope and rise), or to a distance of 200 nautical miles from the territorial sea baselines where the outer edge of the continental margin does not extend up to that distance (http://www.un.org/Depts/los/clcs_new/clcs_home.htm).
When a coastal state’s continental shelf extends beyond 200 M, the state may establish the outer limits of its continental shelf by submitting particulars of such limits to the Commission on the Limits of the Continental Shelf (CLCS). The regime prescribed for the outer limits of the continental shelf where it extends beyond 200 M is contained in Part VI (articles 76 to 85) of UNCLOS. There are several conditions which a coastal state needs to meet in order to submit a claim of extended continental shelf beyond 200 M. A diagrammatic illustration of these conditions is given below.
The Convention also makes an exception to these criteria for the continental margins of the coastal States in the southern part of the Bay of Bengal (“Statement of Understanding concerning a specific method to be used in establishing the outer edge of the continental shelf” adopted by the Third United Nations Conference on the Law of the Sea on the 29th August 1980).
Once a coastal state submits the requisite documentation to the CLCS, which is a 21 member UN body of experts on geology, geophysics and hydrography, all thesubmittedmaterial is thoroughly examined and recommendations are made in accordance with article 76 or the Statement of Understanding, as the case may be.
Considering that India’s continental shelf extends beyond the 200 nautical miles from the territorial sea baselines, the Ministry of Earth Sciences (MoES) undertook a major multi-institutional national programme of collecting, processing, analyzing and documenting the requisite scientific and technical information for delineating the outer limits of the continental shelf in the Arabian Sea and the Bay of Bengal including the western offshore areas of the Andaman-Nicobar Islands. The task was implemented by National Centre for Antarctic and Ocean Research, an autonomous institute of Ministry of Earth Sciences with close participation of Ministry of External Affairs, Naval Hydrographic Office of Ministry of Defence, National Institute of Oceanography and National Geophysical Research Institute of Council of Scientific and Industrial Research, Geological Survey of India, Directorate General of Hydrocarbons, and Oil and Natural Gas Corporation.
In one of the largest ever marine geophysical surveys conducted by India, over 31,000 line km of multichannel seismic reflection, gravity and magnetic data together with bathymetric information were acquired along 42 pre-determined profiles. In the second phase of data collection, around 10,000 line km of multichannel seismic reflection data was acquired. Apart from this, a total of 110 Ocean Bottom Seismometers (OBS) have been deployed so far with a significant retrieval rate of 92% and high quality wide angle seismic reflection and refraction data were obtained at critical locations. A collage of marine survey vessel, equipment and participants from NCAOR is shown below.
The reflection data was utilised to derive the depth to the basement along the different profiles through a process of iterative modelling of the two-way travel time of the acoustic signals passing through the water and the sediments and sedimentary rocks occurring above the basement. From this information and the knowledge of the depth to the seabed, the thickness of the sediments above the basement at thousands of discrete points along these profiles was calculated. On the other hand, OBS data was used to constrain the velocity information obtained from the reflection surveys; and the magnetic and gravity data were utilised to gather additional evidence on the nature of the basement.
The entire data acquisition programme comprising of two phases was implemented during the year 2002-2004 and 2014-15. This was followed by the processing of data, its interpretation with rigorous quality checks and analysis. While the scientific and technical information gathered would serve its primary purpose of delineating the outer limits of India’s continental shelf beyond 200M, the surveys have also furnished invaluable data that could form the cornerstone of the country’s planned endeavours in the oceanic realm.
On the 11th May, 2009, India filed to the CLCS, her first partial submission under the provisions of article 76 for a continental shelf extending beyond 200 nautical miles (M) from the Indian baselines (http://www.un.org/Depts/los/clcs_new/submissions_files/submission_ind_48_2009.htm).
Marine Geophysical Database
Considering the huge volume of geo-scientific data collected as a part of the program and its intrinsic value, the National Marine Geo-scientific Data Center (NMGDC)was established at NCAOR in 2009. The Data Centre allows for a web-based geospatial database of the marine geophysical and bathymetric information pertaining to the Indian continental shelf. The metadata functionality of the database describes the primary details in terms of when and how the data was collected, the nature of data, how the data was processed, necessary supporting information that went in to the processing etc. This endeavour was well appreciated and even awarded for excellence by the Computer Society of India (CSI) in 2009. In 2015, the NMGDC was yet again awarded under the Sustenance category by the CSI due to its efficient functioning and management over a span of 7 years.