南海北部卫滩区浅断层的特征

THE FEATURES OF SHALLOW FAULTS IN WEITAN AREA,NORTHERN PART OF SOUTH CHINA SEA

南海北部卫滩海区的浅层断裂十分发育。主要有NW－NWW、NEE和近EW向三组，它们一般切穿中更新统一上更新统，距离海底深度仅20－50m；有的切穿第四系，直达海底，具有明显的新生活活性，反映了区内剧烈的新构造运动。浅断层的形成，与来自海洋方向的热沉降效应有关，并统一调整于周缘构造应力场的变动。浅断层的活动以断块垂直差异升降为主，促使了大陆边缘的伸张沉降，并严重破坏浅层沉积或引起位移，造成不稳定的工程地质条件。

Large number of shallow faults exist in Weitan area in the northern part of South China sea, mainly trending NW-NWW, NEE and approximatly EW. Generally, they penetrate through middle Pleistocene-upper Pleistocene, and the distance to the floor is only 20~50m. Some faults penetrate through Quaternary, reaching the sea floor. Their obvious Quaternary activity reflects the intensive neotectonism within the area. The formation of the shallow faults was associated with the thermal- subsidence effect from the ocean and unified to the adjustment of variation of the peripheral tectonic stress field. The activity of shallow faults are mainly characterized by the vertical differential elevation and subsidence of fault blocks, which facilitated the extension subsidence of the continental margin, and severely destroyed the shallow sedimentation or caused displacements, resulting in the unstable conditions for engineering geology.