ON THE HANJIANG-DANJIANGKOU RESERVOIR EARTHQUAKES

The Hanjiang-Danjiangkou Keservoir is composed of two parts, the Dan River and Han River Reservoirs. In the gorge district of the Dan River Reservoir, the limestone area consists of well-developed faults and joints, favourable to the permeation and circulation of water.After impounding of water in November 1967, seismicity increased with the changes of water level. The earthquake magnitude of the past few years rose from Mss=4.7 and three earth-quake clustered areas, elongating in the NNW direction were formed near the gorge district of the Dan River Reservoir. Earthquake frequency and intensity correlate to certain extent with the change of water level in the reservoirs.Obvious crustal deformation was observed after filling up of the reservoirs. Distribution of the stress field causing the deformation and the mechanism of earthquake inducing are discussed.