Induced earthquakes in Zhelin reservoir, China

Abstract

Zhelin reservoir is located in an area in East China where the seismic activity is very weak and the frequency of earthquakes is also very low. In the 371 years before the impounding of Zhelin reservoir (1600–1971) there were only five felt earthquakes within a range of 30 km from the lake. After impounding the seismic activities have increased noticeably. There were four sensory earthquakes (the largest one of M s 3.2) and some microquakes over a period of 7 years from 1972 to 1979. During the first 4 years there was certain corresponding relations between the seismic activity and the reservoir level. The events were considered as reservoir-induced earthquakes, although they were of low frequency and magnitude. They were mainly distributed over an active normal fault with a strike-slip on the fringe of the lake. This fault was the seismic structure for the felt earthquake in 1967. Although these induced earthquakes were caused by the dislocation of the active fault they were related to such contributing factors as the softening of the ground mass by water, the effect of pore pressure and the additional stress from the deformation of the reservoir base.