The Tectonic Conditions of Shanxi Reservoir Induced Earthquake in Wenzhou

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).