THE FEATURES OF STRONG EARTHQUAKE ACTIVITY IN NORTH PART OF QINGHAI-TIBET PLATEAU OF CHINA

Using seismological methods we have studied some features of strong earthquake activity in north part of Qinghai-Tibeit Plateau of China. The features are as the following: (۱) The average seismic active time interval is ۲۳۰-۲۵۰ years, and the tranquil period is ۱۳۰-۱۵۰ years; (۲) The earthquake with M ۷۷.۰ occurred at north and south bounderies of the studied area alternatively. In several years before the earthquake with M۷۷, the shocks with ۵.۰۴M<۷.۰ or M-۶ show a feature of gathering distribution. The fault where the first shock with M۱۶.۰ occurred in each period would be the place the earthquake with M۷۷.۰ occurrs later on; (۳) During the three years before an earthquake with MW. ۷ , the moderate earthauakes occurred hardly, but when M<۷.۷ the middle earthquake occurred actively in the area (۴) .There is a correlation of earth-quake activity between the studied area and south boundary of Himalayas or south part of Qinghai-Tibet Plateau