SOME CHARACTERISTICS OF SEISMICITY IN GANSU REGION AND ITS SIGNIFICANCE
WANG Zhouyuan JI Fengying (Earthquake Research Institute of Lanzhou,SSB,Lanzhou 730000)
About 32 months quasi periodicity was clearly shown in activity of M S≥3.0 earthquakes in Gansu region.The great shocks with M S≥6.0 in and near the region occurred near the valley of annual frequency curve of M S≥3.0 earthquakes. Since 1980,moderate shocks in Gansu region migrated regularly and steadily in groups from west to east along the northern edge of Qinghai Xizang block.The migrations show clearly that seismicity in current period has been at a low ebb now,and may enter on a quiet phase in about the year 2002.There will be a seismic activity of M S≥5.5 at about the end of the year 1998 in the Gansu region and its vicinity. That the moderate events of M S≥5.0 occurred at the west end of northern edge of Qinghai Xizang block is a signal of the beginning of active process of strong moderate earthquakes in Gansu region.