丹江口水库区地震的形成条件与发展趋势的讨论

A DISCUSSION ABOUT THE FORMING CONDITIONS AND DEVELOPING TREND OF THE EARTHQUAKE IN THE DANJIANGKOU RESERVOIR AREA

摘要:

本文对丹江口水库区地震活动的有利地质条件,海西期以来应力场,地震活动特点,成因与发展趋势都作了讨论。初步认为:丹江口地震活动区处在两组不同的构造线交汇,隆起断块与下降断块接触边缘,差异运动强烈地段以及不同类型岩石的接触部位。地震活动是在特殊水文地质环境下,由于北东东向压应力作用,两组剪切面在水的参与下发生滑动的结果。有利的地质条件是丹江口水库区地震活动的主因,库水引起的垂直压力和孔隙压力是次要因素。在发展趋势上,1973年11月29日4.7级地震可能就是157米水位线诱发的最高震级。二期工程竣工后,有可能发生5级左右的地震。这一看法,对充分利用丹江口水库使其发挥应有的作用,以及二期工程的进行都可能有一定的参考价值。

Abstract:

In this paper, the favourable conditions of the earthquake activities in the Danjiangkou reservoir area, stress field since Hercynian period, characteristics of Seismicity, cause of its formation and its developing trend are discussed. Our tentative consideration is that, the occurrence of the earthquake activities is due to its different situations and different conditions, i. e. 1.It lies on the intersecting line of two groups of different structure, on the contact border of uplift and subsiding rift blocks and in the section of strong differential movement, which is the contact position of rock in different types; and 2. It occurs under special hydrogeological environment and the action of compressive stress in a direction of NEE and slips owing to its water permeating into two groups of shear surface. The major reason of the earthquake activities in the Danjiangkou reservoir area is its favourable geological conditions. The water in the reservoir gives rise to vertical and pore pressures is the secondary reason. As to the developing trend, the earthquake of Ms=4.7 occurring in November 29, 1973 may be the highest magnitude induced by a water level line to 157 meters high. An earthquake of Ms=5 will possibly occur when finishing the project in the second period. This point of view will be worth certain reference to fully utilize and bring into play the effect of the Danjiangkou reservoir and is favourable for constructing the project of the second period.