Abstract
The margins of the continents or transition zones between continents and oceans are divided traditionally into two types: Atlantic and Pacific. There are also some transition types between these two.
From the geophysical point of view the border between a continent and an ocean is determined now as an area where changing the crust from continental type to oceanic one is observed.
Atlantic type is characterized by abruption of continental structure spreading from the shore to the shelf with the border of the bottom on the deep ocean. The area of changing the crustal type is not so wide, about 50-150km.
Pacific type is much more complicated and includes not only structures typical for Atlantic type but also such specific ones as marginal seas, island arcs with active volcanoes and deep oceanic trenches. The trend line of the border of the deep oceanic bottom is usually parallel to the trend line of the geological structure of marginal zones and adjoint lands.
Geophysical data on the deep crustal structure of the transition zones are scattered up to day still. Nevertheless many important regularities were observed last decade. The reverse relationship between the oceanic and sea depths and the thickness of the crust is the most certain regularity. We observed considerable decreasing the crustal thickness in comparison with that on the adjoint land just near the shore where water depth on the shelf was only some hundred meters. But this relationship is quite certain for the large underwater structures and breaks down usually at the transition zones.
