Abstract: In accordance with the requirements of "Eleventh Five-Year" national scientific and technological support projects,an intensive seismic observation network consisting of 26 seismic stations was established at the Three Gorges Reservoir area in the section of Hubei Province in March 2009(21 short-period seismographs,5 broadband digital seismographs).From March to December,2009,2995 M_L-0.8～2.9 earthquakes were observed during the trial impounding of the Three Gorges Reservoir(water level rose from 145m to 172.8m).Using the double difference earthquake location algorithm,2837 earthquakes were relocated precisely.The results show: The pattern of small local earthquake swarms in Three Gorges Reservoir area took on a linear distribution or mass-like cluster distribution,the mass-like clusters of events were generally within the distance of 5km from waterfront,and the linear distribution of the earthquakes could be extended to a distance of 16 kilometers away from waterfront.In Hubei section of Three Gorges Reservoir,earthquakes were mainly concentrated in the northern end of Xiannüfeng and Jiuwanxi Fault in the vicinity of the Xiangxihe river,and along the banks of the Yangtze river at the east of Xietan village and at Shenlongxi area on the northern bank in Badong region;the focal depths were less than 10km,and 4km in average.Earthquake frequency of the reservoir region had a positive correlation with reservoir water level fluctuation,indicating that the seismicity belonged to the reservoir induced earthquakes.Along the Shenlong river in the reservoir area,earthquakes showed three linear distributions in the northern Badong County,which was related to karst distribution.There are underground rivers along carbonate strata.When reservoir was impounded,water permeated into the underground rivers,thus inducing earthquakes.Earthquakes in the areas on the cross-river segment of Xiannüfeng Fault,the Jiuwanxi Fault and at the areas west of Xietan,Shazhen and Xizhen,may be related to the softening of discontinuities,such as the Nukou Fault,the Xiannüfeng Fault or the bedding joints,etc.,which would lead to failure of rock masses,thus,inducing earthquakes.However,convincing conclusions about the triggering mechanism still need further study.In addition,in the areas south of Wenhua and Yanglin of Zigui County and at Rangkou town east of Badong county,there are mining-induced earthquakes at the mines nearby.And on the shores of the reservoir,there are some collapse earthquakes.

Key words: reservoir-induced seismicity, observation, earthquake location, seismogenesis, Three Gorges reservoir of Yangtze river

摘要： 从2009年3月起在长江三峡水库湖北段建立了26个地震台站组成的加密台网。2009年3—12月记录到2995次M_L-0.8～2.9地震。利用双差定位软件重新确定了2837次地震的精确位置。结果显示:长江三峡水库库区小震震群分布图像呈线性分布或团块状丛集分布,团块状丛集一般在距离库水边5km范围内,地震线性分布可以延伸到距库水边16km远的地方;长江三峡水库湖北段地震主要集中分布在香溪河附近的仙女山断裂北端及九湾溪断裂、泄滩乡以西的长江两岸和巴东北岸神龙溪及附近地区,震源深度<10km,平均在4km左右;库区地震活动频次与库水位升降过程正相关,说明属于水库诱发地震。巴东库区神龙溪两岸地震明显呈现出3条线性分布,通过对比该地区碳酸盐岩的分布特征,发现是由于水库蓄水后,库水从神龙溪两岸等地下暗河渗入而诱发地震的;而仙女山断裂过江段、九湾溪断裂和泄滩乡、沙镇溪镇西部地区等的地震可能与仙女山断裂带、牛口断裂或顺层解理等不连续结构面软化,导致岩体失稳而诱发了水库地震,但诱发机制仍需要进一步详细研究才能获得令人信服的结论。另外,在秭归县文化南和杨林、巴东县东壤口镇以东等地存在着煤矿开采引起的矿山诱发地震,在长江三峡库区两岸存在着一些塌陷地震。

关键词: 水库诱发地震, 观测, 地震定位, 成因, 长江三峡水库