浙江湖南镇水库的诱发地震

1982年和1983年汛期在水库地震区设立密集地震台网。观测表明,地震群集在水库近岸,深度仅几百米。地震与库水位的急剧升降几乎同时出现。几百次单个地震的震源机制解显示出以逆断层和正断层机制为主。地震是库水渗入后在库岸局部应力和岩体重力作用下沿小断层、节理错动的结果,发生破坏性地震的可能性很小

INDUCED SEISMICITY AT HUNANZHEN RESERVOIR,ZHEJIANG PROVINCE

Hunanzhen reservoir with a dam 129m high and a volume of 2×109m3 is located in Quxian County,Zhejiang Province.A series of tremors have occurred since its impoundment in 1979.A dense seismic network was installed in the epicentral area during high water season of 1982 and 1983.Hypocenters of 1029 were located and focal mechanism for 372 events was individually determined.The observations show that almost all of the events are clustered along the immediate banks upstream 15km from the dam and have quite shallow depth only of hundreds of meters.Seismic activities bursted with rapid fluctuation of lake level only in hours to days' delay.Focal mechanisms demonstrate that most are of thrust fault and next the normal.Analysis of the data suggests that the seismicity is caused by the slips along the preexisting fractures due to the water seeping under the effect of local stress in the banks or the gravitation of rock mass.Future seismic activity is expected to be continued for a time but to be limited in magnitude