Prof. Dhammika A. Tantrigoda and Dr. M. M. P. Madhuranga Fernando
Department of Physics, University of Sri Jayewardenepura, Gangodawila, Nugegoda

In this study, variations of the gravity field over the Indian Ocean region around Sri Lanka, have been interpreted using well-established inversion techniques in Geophysics. In the interpretation, special attention was paid to the regions covering the continental shelf and slope of Sri Lanka, Bay of Bengal having several large sea mounts, 85o E ridge and the region below the 5o S of the equator where no significant geophysical work has been carried out. Sediment thickness over the above regions has been estimated and a sediment thickness map covering the region 79oE-86oE, 2oN-8oS was compiled. Position of the foot of the continental shelf of Sri Lanka was also determined.



Gravity Anomalies over the central Indian Ocean in mGals



Sediment thickness over the Indian Ocean region surrounding Sri Lanka as revealed by the study

Rationale of the study stems from the usefulness of its outcome for delimitation of the outer edge of the continental margins of Sri Lanka according to the provisions of the United Nations Convention of the Law of the Sea (UNCLOS). According to the Annex II of the Final Act of the UNCLOS, Sri Lanka can claim the sea area up to a boundary where sediment thickness is 1 km.   Multi-channel seismic techniques have been recommended as the most suitable method for delimitation purposes by the technical guidelines issued by the UNCLOS. However, this method is very expensive as cost of seismic vessels is very high. Therefore it is cost effective to first estimate an approximate delimitation boundary using inexpensive method such as interpretation of gravity anomalies and then carry out the seismic survey over a narrow region around the approximate boundary and determine a more accurate boundary. Sediment thickness information provided by this study has been used by the DEOCOM project, project that is in charge of delimiting the continental margins of Sri Lanka, in planning the cruise tracks of the survey vessel that carried out the seismic survey.  This information is also useful in illustrating continuity of sediments in the Indian Ocean around Sri Lanka, a criteria needed to be established in Sri Lanka submission to UNCLOS.

Further, the sediment thickness information estimated, especially over the continental shelf and slope of Sri Lanka is useful in identifying sedimentary basins, which have a potential of accumulating mineral oil.