A PRELIMINARY STUDY ON PALAEO-EARTHQUAKE EVENTS OF THE REISHUI-RIYUE MT. ACTIVE FAULT ZONE IN QINGHAI PROVINCE

Reishui-Riyue Mt. active fault zone is a very important NNW oriented rightlateral strikeslip active fault zone which developed in the Chaidam-Qilian Mt. active crustal block,northeastern margin of Qinghai-Tibet Plateau.The activity of the fault causes a series of microgeomorphologies,such as ridge, valley and terrace,rightlateral offseted and forms fault cliff and fault scarp et al. vertical offset microgeomorphology.In this paper,the palaeoearthquake events on the fault are studied.Combining the trench profiles and fault scarp measurement,two palasoearthquake events are determined,which occured in 6 280±120 a B.P. and 2 220±360 a B.P.,the recurrence interval is about 4 000 a.