Abstract:

Basing on geological field investigation and other relevant data,this paper analyzes the geologic-tectonic features,seismic activity background,regional stress field and hydrogeologic conditions of the Jinanqiao reservoir area. Moreover,the comparison with the other reservoirs of the similar conditions has been carried out. The results indicate that induced earthquake is possible to occur in the Jinanqiao Reservoir of the Jinshajiang River. The bedrock in the dam site to Guoshi segment of the reservoir consists of basalts produced by multicycle eruptions in Permian period. Joints and cracks in the basalt are mainly south-north-trending,consistent with the orientation of the principal regional compressive stress. Under the action of regional stress field,these fissure systems will propagate and enhance the percolation of water. As a result the stress produced by the mountain and rock mass would significantly increase when the water is stored in the reservoir. In consideration of the activity of the Shudi fault,it is calculated by probability method that the probability of the occurrence of type-Ⅰ induced earthquake in this segment is 2‰,that of type-Ⅱ induced earthquake is 5%,and that of type-Ⅲ induced earthquake is 20%. Therefore,an induced earthquake of magnitude 5.0 is possible to occur in the vicinity of Shudi. The bedrock in the Guoshi to Paimai segment of the reservoir consists mainly of limestone and dolomitic limestone,and karsts are well developed in the canyon area of this segment. At the intersection of faults in the vicinity of Guoshi,Huangyangguo and Wajinping,an induced earthquake with maximum magnitude of 5.0 is possible to occur. In the other places of this segment induced earthquake of magnitude 4.0 is possible to occur owing to the development of karsts,joints and fractures. Probability calculation shows that the probability of type-Ⅰ induced earthquake in this segment is 3‰,that of type-Ⅱ induced earthquake is 9%,and that of type-Ⅲ induced earthquake is 20%. The bedrocks in the segment from Paimaidang to the tail of the reservoir are relatively complex. The karstification in this segment is relatively weak owing to shallow water level and the existence of impure limestone and insoluble interbeds of sandstone and shale,so that the percolation of water in this reservoir segment is relatively weak. The probability of the occurrence of type-Ⅰ and type-Ⅱ induced earthquake is very low,and that of type-Ⅲ induced earthquake is lower than that in the other segments of the reservoir. However,the probability of type-Ⅳ induced earthquake is rather high,i e. there is high possibility of the occurrence of induced earthquake of magnitude 3.0. Comprehensive analysis of the probability of induced earthquake in Jin'anqiao Reservoir indicates that induced earthquake that may damage the hydraulic structures is impossible to occur in the basaltic segment and the head of the reservoir. However,induced earthquake of magnitude 5.0 is possible to occur at the intersection of faults in Shudi,Wajinping,Huangyangguo and Guoshi area,and the epicentral intensity may reach Ⅶ. The intensity affected to the dam buildings will be Ⅵ. Induced earthquake with magnitude 3.0 is possible to occur along the carbonate segment from Paimaidang to the tail of the Reservoir,but the damage effect of this earthquake can be neglected.

Key words: induced earthquake, reservoir, probability, Jin’anqiao

摘要：

金安桥水库区按地质构造、岩性、区域应力场、地震活动背景及水文地质条件,可分为3个库段。从坝址区到果世库段的岩性为玄武岩,主要断裂有三古断裂、楚夺洛断裂、树底断裂。在坝址到果世库段的树底和果世附近,果世至排卖当碳酸盐岩库段的瓦金坪、黄洋沟附近有发生5.0级地震的可能,震中烈度可达Ⅶ度。排卖当至库尾的碎屑岩库段不会发生水库诱发地震,其中碎屑岩中夹的碳酸盐岩段有发生3.0地震的可能性,烈度<Ⅵ度。

关键词: 金安桥水库, 诱发地震危险性评价, 诱震条件, 水库地震影响烈度