Intensive Observation of Reservoirinduced Seismicity and Preliminary Analysis on the Causes of Earthquakes in the Three Gorges Reservoir Area,Yangtze River

In accordance with the requirements of the National Key Technology R＆D Program of the 11th ＂Five-year Plan＂, a densified seismic 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, a total of 2,995 ML -0. 8 - 2. 9 earthquakes were detected during the trial impounding of the Three Gorges Reservoir （ water level rose from 145 m to 172.8m）. Using the double difference earthquake location algorithm, 2,837 earthquakes were precisely re-located. The results show that the pattern of small local earthquake swarms in the Three Gorges Reservoir area took on a linear distribution or mass-like cluster distribution, the mass-like clusters of events were generally within a distance of 5 km from waterfront, and the linear distribution of the earthquakes could be extended to a distance of 16 km away from the waterfront. In the Hubei section of the Three Gorges Reservoir, earthquakes were mainly concentrated in the northern end of the Xiannvshan and Jiuwanxi faults near the Xiangxihe River, and along the banks of the Yangtze River at the west of Xietan township and the Shenlongxi area on the northern bank in the Badong region, with focal depths less than 10km, and 4km in average. Earthquake frequency in the reservoir region had a positive correlation with reservoir water level fluctuations, indicating that the seismicity belongs to reservoir induced earthquakes. Along the Shenlong River in the reservoir area, earthquakes showed three linear distributions in the northern Badong county, and distributed according to Karst distribution. There are underground rivers in the carbonate strata. When the reservoir was impounded, water permeated into the underground rivers, thus inducing earthquakes. Earthquakes in the areas on the crossriver segment of Xiannvshan 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 Xiannvshan fault, or the bedding joints, which would lead to failure of rock masses, thus, inducing earthquakes. However, convincing conclusions about the triggering mechanism still need further study. Additionally, near the areas south of Wenhua and Yanglin of Zigui county and at Rangkou town east of Badong county, mininginduced earthquakes occurred at the mines nearby, and on the shores of the reservoir are some collapse earthquakes.

根据第 11 五年的计划的国家关键技术 RD 节目的要求，由 26 个地震车站组成的一个使增加密度的地震网络在 2009 年 3 月 21 短时期的地震计在湖北省的节在三个峡水库区域被建立， 5 宽带数字地震计。从三月到 2009 年 12 月， 2,995 ML -0 的一个总数。8 - 2。9 地震在从 145 m 三朵峡水库水水平玫瑰扣押到 172.8m 的试用期间被检测。用双差别地震地点算法， 2,837 地震精确被重定位。小本地地震的模式聚集在三个峡水库区域的结果表演呈现了线性分布或像团的簇分发，事件的像团的簇通常在从水滨的 5 km 的距离以内，并且地震的线性分发能被扩大到 16 km 的距离离开水滨。在三座峡水库的湖北节，地震主要在 Xiangxihe 河附近在 Xiannvshan 和 Jiuwanxi 差错的北结束被集中，并且沿着在在 Badong 区域的北河岸上的 Xietan 镇区和 Shenlongxi 区域的西方的长江的河岸，与焦点的深度不到 10km ，和 4km 在平均。在水库区域的地震频率与水库水水平变化有积极关联，显示 seismicity 属于水库导致的地震。沿着在水库区域的 Shenlong 河，地震在北 Badong 县显示出三线性分布，并且根据石灰岩地区常见的地形散布了分发。在碳酸盐阶层有地下的河。当水库被扣押时，水渗入了进地下的河，因此导致地震。在 Xiannvshan 的 crossriver 片断上的区域的地震指责， Jiuwanxi 差错并且在 Xietan ， Shazhen 和 Xizhen 的区域西方，可能与弄软断绝有关 Xiannvshan 差错，或床上用品例如 Nukou 差错，连接，它将导致岩石群众的失败因此，导致地震。然而，关于被触发的机制的有说服力的结论仍然需要进一步的学习。另外， Zigui 县并且在 Badong 县的 Rangkou 镇东方的 Wenhua 和 Yanglin 向南接近区域， mininginduced 地震在水库的岸是的附近，并且上的矿发生了一些倒塌地震。