<P> Under the United Nations Convention on the Law of the Sea, the name continental shelf was given a legal definition as the stretch of the seabed adjacent to the shores of a particular country to which it belongs . </P> <P> The width of the continental shelf varies considerably--it is not uncommon for an area to have virtually no shelf at all, particularly where the forward edge of an advancing oceanic plate dives beneath continental crust in an offshore subduction zone such as off the coast of Chile or the west coast of Sumatra . The largest shelf--the Siberian Shelf in the Arctic Ocean--stretches to 1,500 kilometers (930 mi) in width . The South China Sea lies over another extensive area of continental shelf, the Sunda Shelf, which joins Borneo, Sumatra, and Java to the Asian mainland . Other familiar bodies of water that overlie continental shelves are the North Sea and the Persian Gulf . The average width of continental shelves is about 80 km (50 mi). The depth of the shelf also varies, but is generally limited to water shallower than 150 m (490 ft). The slope of the shelf is usually quite low, on the order of 0.5 °; vertical relief is also minimal, at less than 20 m (66 ft). </P> <P> Though the continental shelf is treated as a physiographic province of the ocean, it is not part of the deep ocean basin proper, but the flooded margins of the continent . Passive continental margins such as most of the Atlantic coasts have wide and shallow shelves, made of thick sedimentary wedges derived from long erosion of a neighboring continent . Active continental margins have narrow, relatively steep shelves, due to frequent earthquakes that move sediment to the deep sea . </P> <P> The shelf usually ends at a point of increasing slope (called the shelf break). The sea floor below the break is the continental slope . Below the slope is the continental rise, which finally merges into the deep ocean floor, the abyssal plain . The continental shelf and the slope are part of the continental margin . </P>

Which one of the most extensive part of the oceanic floor