均衡异常与现代构造应力场的初步研究——以东海及其东缘海为例

PRELIMINARY STUDY ON ISOSTATIC ANOMALY AND RECENT TECTONIC STRESS FIELD——TAKING EAST SEA AND ITS EASTERN BOUNDARY SEAS AS EXAMPLE

从现代构造运动的实际出发,放弃了过去那种只认为因补偿过剩和补偿不足的均衡调整的观点,探讨了引起不均衡的构造应力,并视均衡异常为地球内部的一种负荷,由此可以计算得到地球内部的应力.研究结果表明:东海及其东缘海地区由均衡重力异常推求的垂向应力的变化比水平应力更为显著,在琉球海沟一带存在5 MPa垂向应力的增强,它明显地反映了板块俯冲的作用.在海沟西北侧的岛弧一带的应力状态则与之相反,约存在5 MPa的垂向应力减弱.东西两部分的水平应力在方向上有明显的不同,洋壳上的东西向应力sx为负(压力为正),而陆壳上则相反.这正表明了板块间相互挤压的作用.

On the basis of the reality of recent tectonic movement and discarding such a viewpoint that the isostatic adjustment only results from excessive or insufficient compensation we have discussed the tectonic stress causing inequality and regard the isostatic anomaly as a load on the earth抯 interior, thus the earth抯 inner stress can be calculated. The research results show that in the East Sea and its eastern boundary seas area the change of the vertical stress derived from the isostatic gravity anomaly is more marked than that of the horizontal stress. Along the trench there is an enhancement of vertical stress by 5 MPa, which evidently reflects the effect of plate subduction. On contrary, along the island arc to the northwest of the trench the vertical stress weakens by about 5 MPa. The horizontal stresses in eastern and western parts are obviously different that the east-westward stress on the oceanic crust xs is negative (while the pressure is positive) but on the continental crust is positive. These facts indicate the effect of compression between plats.