温州珊溪水库诱发地震构造条件

The Tectonic Conditions of Shanxi Reservoir Induced Earthquake in Wenzhou

自2002年7月温州珊溪水库首次发生地震后,其地震活动持续至今,但目前人们对水库地震成因了解较少.基于对库区所处的区域地震地质背景、库区地形地貌、岩性及新构造运动特征的分析,采用野外地质调查的方法,获得了库区主要断层的地质特征,并评价了其渗透性.在此基础上,结合地震活动特征及震源机制解的研究成果,探讨了水库地震时间序列及发震机理.结果表明珊溪水库地震活动与库区岩性、断层(尤其是库区内的双溪-焦溪垟断层)及库水特征关系密切.水库地震主要发生在侏罗系凝灰岩夹砂岩、泥岩等隔水性好的层状岩层中,而渗透性较好的双溪-焦溪垟断层结构面则更利于库水下渗,这种岩体结构面组合方式一方面使库水容易沿断层结构面向深部渗透,另一方面断层结构面上的孔隙压力容易升高,因此降低了断层结构面上的正应力,应力平衡被打破,进而诱发地震.在水的渗透和地震活动的相互作用下,水库地震沿双溪-焦溪垟断层(尤其是第三分支断层)从SE向NW持续发生.

The Wenzhou Shanxi reservoir-induced earthquake has been active since its first occured in July 2002.However,less is known about the genesis of Shanxi reservoir-induced earthquake.Based on the analysis of regional seismic geological background,reservoir topography,geomorphology,lithology and new tectonic movement characteristics,the reservoir area＇s geological characteristics of the main faults were obtained and its permeability was evaluated by using field geological survey method.On this basis,time series and mechanism of the earthquake were discussed in combination with the study of seismicity and focal mechanism solutions.Finally we concluded that the earthquakes activities in Shanxi reservoir were closely related to the lithology,fault（especially the Shuangxi-Jiaoxiyang fault）and water in the reservoir.The earthquakes occurred mainly in Jurassic sandstone,mudstone rock tuff,etc.which belong to aquifuge tuff,while the structure plane in Shuangxi-Jiaoxiyang fault is beneficial to the infiltration of the reservoir water.This combination of rock mass structural plane induced,on the one hand,easy infiltration of the reservoir water to the deep underground through the fault,on the other hand,the increase of pore pressure on the fault structure plane.Therefore,the normal stress was reduced on the fault structure plane,and the stress balance was broken,which induced the occurrence of the earthquake activities finnally.Under the double influence of water infiltration and earthquake activity,the earthquakes contiuously occured from southeast to northwest along the Shuangxi-Jiaoxiyang fault（especially the third branch fault）.