3D numerical techniques for determining the foot of a continental slope

[摘要] ENGLISH ABSTRACT:The United Nations Convention on the Law of the Sea (UNCLOS) provides an opportunity for qualifying coastal signatory states to claim extended maritime estate. The opportunity to claim rests on the preceptthat in certain cases a continental shelf extends beyond the traditionally demarcated two hundred nauticalmile (200M) Exclusive Economic Zone (EEZ) mark. In these cases a successful claim results in stateshaving sovereign rights to the living and non-living resources of the seabed and subsoil, as well as thesedentary species, of the area claimed. Where the continental shelf extends beyond the 200M mark, theFoot of the Continental Slope (FoS) has to be determined as one of the qualifying criteria. Article 76 ofUNCLOS de nes the FoS as . . . the point of maximum change in the gradient at its base. CurrentlyCaris Lots is the most widely used software which incorporates public domain data to determine theFoS as a step towards defining the offshore extent of an extended continental shelf. In this software,existing methods to compute the FoS are often subjective, typically involving an operator choosing thebest perceived foot point during consideration of a two dimensional profile of the continental slope.These foot points are then joined by straight lines to form the foot line to be used in the desk top study(feasibility study). The purpose of this thesis is to establish a semi-automated and mathematically basedthree dimensional method for determination of the FoS using South African data as a case study.Firstly, a general background of UNCLOS is given (with emphasis on Article 76), including a briefdiscussion of the geological factors that influence the characteristics of a continental shelf and thusfactors that could influence the determination of the FoS.Secondly, a mathematical method for determination of the surfaces of extremal curvature (on threedimensional data), originally proposed by Vanicek and Ou in 1994, is detailed and applied to two smooth,hypothetical sample surfaces. A discussion of the bathymetric data to be used for application introducesthe factors to be taken into account when using extensive survey data as well as methods to processthe raw data for use. The method is then applied to two sets of gridded bathymetric data of differingresolution for four separate regions around the South African coast. The ridges formed on the resultingsurfaces of maximum curvature are then traced in order to obtain a foot line definition for each regionand each resolution.The results obtained from application of the method are compared with example foot points providedby the subjective two dimensional method of computation within the Caris Lots software suite. Acomparison of the results for the different resolutions of data is included to provide insight as to theeffectiveness of the method with differing spatial coarseness of data.Finally, an indication of further work is provided in the conclusion to this thesis, in the form of anumber of recommendations for possible adaptations of the mathematical and tracing methods, andimprovements thereof.

[发布机构] Stellenbosch University