Page - 463 - in Book of Full Papers - Symposium Hydro Engineering

SUMMARY The odds of extreme weather events increased significantly recently against the backdrop of global climate change, in which China is one of the most affected countries especially for typhoon and rainstorm. The water level will change rapidly if the typhoon or rainstorm occurred in the reservoir region, which is seemed to increase the occurrence probability of Reservoir-Induced Seismic (RIS). The RIS means typically minor earthquake sequence resulting from reservoir impoundment or variation of water level. The damage of RIS may probably be much bigger than that of natural earthquake because its focal depth is very shallow. Therefore, it is necessary to study the mechanism of extreme weather induced RIS events, as well as provide some corresponding countermeasures for reservoir operation management. Shanxi reservoir is located in the upper stream of Feiyun river (Zhejiang Province, China) with capacity of 18.24×108m3, and the height of the concrete face rockfill dam is 156.8m. Shanxi reservoir region will be affected by typhoon from June to September every year. The impoundment of the reservoir started from May 12th, 2000. From that time on, the induced seismic activity has been an issue for the Shanxi reservoir. In this study, a seismic catalogue contains 5908 records are used to study the seismic activity of Shanxi reservoir region (27°60’～27°80’ N, 119°80’～120°10’E), which is recorded from July 2002 to July 2016. Consider the features of seismic activities and geological conditions in Shanxi reservoir, conclusions could be summarized as follows. 1. The seismic frequency of Shanxi reservoir region increases significantly after the impoundment, and the seismic activities shown a periodic change in every 4 years. 2. More than 99% of the seismic events are weak or micro earthquakes, and the maximum magnitude is ML4.6. 3. The seismic events after the impoundment are mainly distributed in the area near fault F2 and F3. 4. The results of double-difference location algorithm suggest that the branch fault F3-3 is the causative fault of 2014 seismic cluster. 5. The preferably infiltration conditions of fault F3 (steep dip and higher permeability) is the control factor of the seismic activity in Shanxi reservoir. At last, we suggest that the changing rate of water level in dam operation should be controlled in a relative low level, especially for the water level decreasing rate must be limited to no more than 2m/day. KEWORDS INDUCED SEISMICITY, RESERVOIR OPERATION, WATER LEVEL 463