摘要
分析了丹江口水库从1967年到1987年的水位及其变化幅度与地震的相关性,分析发现水库蓄水后的诱发地震主要沿丹江断裂分布,并且主要集中在该断裂经过的碳酸盐岩区,说明库区岩石的渗透性,对诱发地震有重要影响;注意到当库区的水位增加到新的较高水位时,常常会引发新的较高等级的地震,并且具有一定的滞后性,这表明孔隙水压力是该库区诱发地震的诱震机制。预计,当丹江口水库二期工程施工完毕,水位增大到170m时,很可能会引发M4级以上地震。根据Roeloffs建立的计算扩散孔隙水压力公式编写一维程序,计算了4个地震震源处的孔隙水压力大小及其日变化率,发现诱发地震时震源处的孔隙水压力约为几百千帕,该值远远低于围压及围岩的强度,表明该区域在蓄水前应处于饱和、临界应力状态。诱发不同强度地震所需要的孔隙水压力大小不同,并且与库区断层的岩性相关。诱发M2级以上的地震的孔隙水压力阈值应在100k Pa以上。孔隙水压力的日变化率值很小,即使在库水位有较大波动时也没有明显上升,表明水位变化幅度与诱发地震关系不大。
Through the analysis of correlations between water levels and seismicity in Danjiangkou Reservoir from 1967 to1987,it was found that the induced seismicity mainly distributed along Danjiang fault,and that the permeability of rocks and faults in reservoir area had important influences on the reservoir induced seismicity. It should be noted that the increase in water levels over the previous highest levels was directly correlated with the increased magnitudes of the induced earthquakes and that there was a lag in time between the high water levels and the occurred earthquakes,indicating that the pore water pressure is the triggering mechanism of induced seismicity in Danjiangkou Reservoir. It could be predicted that when the water level is increased to 170 m during the second construction stage,seismicity with the magnitude over M4. 0 may occur. According to the formula proposed by Roeloffs,a 1D program was written,and the diffused pore pressure and its daily changing rate was calculated in the hypocentral locations of four earthquakes. The results show that the pore pressures in hypocenter locations of four earthquakes are around several hundreds of kilopascal,which are much less than the confining pressure or the strength of rocks,implying that the rocks or faults in the region are in saturated and critical stress states before impounding. The intensity of seismicity induced by the pore pressures may depend on the lithology of defaults. The threshold level for pore pressures which may induce the earthquake more than M2 is not less than 100 k Pa. The daily changes rates of pore pressures are very low,and have no obvious increase even when the high fluctuation in water was observed,indicating that the changing amplitude of water levels has no close correlation with the reservoir induced seismicity.
出处
《土木工程学报》
EI
CSCD
北大核心
2015年第6期89-96,共8页
China Civil Engineering Journal
基金
湖北省自然科学基金(2011CDB267,2012FFC05201)
关键词
孔隙水压力
丹江口水库
水库诱发地震
pore pressure
Danjiangkou reservoir
reservoir induced seismicity
