南海及邻区现代构造应力场初探

A STUDY OF THE MODERN TECTONIC STRESS FIELD OF SOUTH CHINA SEA AND ITS VICINITY

用数学模拟方法对南海及邻区的现代构造应力场及其动力进行定量分析,结果表明南海及邻区现代构造应力场与新构造运动密切相关,现处于一个全面挤压的新阶段,应力差值大小分布呈环带状,主应力方向呈规律分布,南海及邻区的区域稳定性可分为烈、强、中、弱四个活动区,南海北部陆缘地区属中活动区,其活动性质介于被动陆缘和主动陆缘之间。

The modern tectonic stress field of South China Sea and its vicinity as a plane stress problem of elastic plate has been computed by means of the finite element method. Taking trench-subduction zones as major boundaries, the studied region, composed of 5 parts with different crustal thickness, velocity of P-wave, density or Poisson's ratio, is divided into 1130 triangular elements with 612 points. Four models of boundary forces, which represent the forces exerted to South China Sea and its vicinity by Indian Ocean-Australia Plate and Philippine Sea Plate respectively, have been tested. The directions of the maximum compressive principal stress obtained from the calculation have been compared with that of focal mechanism solutions. The model which agrees most satisfactorily with focal mechanism soluticns was selected as the available model. The relationship between modern tectonic stress field and neotectonic movement, the evolutionary history of tectonic stress field, and the regional stability of South China Sea and its vicinity were studied.The results show that the modern tectonic stress field is related closely to neotectonic movement;the spatial distribution of the stress difference appears as a circular zone; the direction of the maximum ccmpressive principal stress is NW-trending in the eastern part,NE-trending in the western part, and NEE-trending in Banda Sea. South China Sea is a continental marginal sea Diwa. The evolution of its tectonic stress field can be divided into four stages, and the present is a new stage of compression. The studied region can be divided into extremely,very,intermediately, and weakly active regions according to stability. The northern continental margin of South China Sea is an intermediately active region, and its activity is between those of active continental margin and passive continental margin.