The paper discusses the significance of proposed ocean drilling sites in the South China Sea (SCS )on the bases of geological and geophysical characteristics of the northern and the southern continental margins and the central basin of the SCS, as well as unresolved tectonic problems for the area.
    The northern continental margin of the SCS is a divergent one. In between the continental and oceanic crusts there is a magnetic quiet zone, with southward thinning upper crust and lower crust. The proposed drilling sites are to investigate the materials underlying the magnetic quiet zone and the nature of this zone.
    The southern continental margin of the SCS is a convergent one, in contrast with the northern margin in structural and geophysical styles. Drillings in the southern margin have been concentrated in the shelf areas to the south. It is necessary to drill the Nansha area (the Dangerous Grounds) in order to understand the tectonic evolution of the entire southern margin. Major objectives of the proposed drilling sites are to study Tertiary and pre-Tertiary stratigraphy and material source of the area.
    In cooperation with the scientists from the Tokyo University,we surveyed the northern portion of the central basin of the SCS with a three-axial magnetometer. Results show magnetic anomalies 11 to 7 with nearly E-W orientation,and anomalies 6 to 5e with a NE orientation. In the SW subbasin of the SCS, magnetic anomalies strike in a NE direction. Drilling sites in these areas are proposed to determine the ages of these magnetic anomalies and the materials of the oceanic crust of the SCS.