“翻台法”提高地震定位精度的数学原理

对于震中偏离台网情况下的地震定位，常规方法定位效果较差。“翻台法”有效地提高了其定位精度。从均匀地壳模型的走时方程组出发，分析了“翻台法”定位中方程组系数的变化特点，推导了选取最佳翻转台站的方法，并得出如下结论：（１）“翻台法”增加了原定位方程组的约束方程，翻台数与已知条件和所求参数个数有关，从理论上讲，翻转台数超过独立的约束方程数时对增加定位精度不再有意义；（２）考虑到具体的台网布局和台站资料质量，翻转不同台站对提高地震定位精度所起的作用大小各不相同，因而存在选取最佳翻转台站问题。

MECHANISM OF INTRAPLATE EARTHQUAKE AND DISTRIBUTION OF GLOBAL SEISMICITY:Explanation of Internal Wave Hypothesis on Seismicity

Some problems with respect to the mechanism of intraplate earthquakes and Benioff zone,which is set up from plate tectonics,are described. Based on the viewpoint of internal wave hypothesis,the mechanism is discussed. It follows from the fact that the gravitational potential energy stored in the difference of crustal thickness makes crustal material move that the internal wave movement which causes the change of cructal thickness leads to the kinds of intraplate earthquakes.The global seismicity distribution along latitude is studied,the results show that it is related with tidal and continental distribution. The continents can not all along be of gravitational isostasy and becoome the active area of crustal movement because of the geologic action of exogenic force such as denudation,transportation,deposition and the redistribution of loads. In addition,the mechanism of deep-focus earthquake and Benioff zone is also discussed on the basis of internal wave hypothesis.