Abstract：An earthquake of magnitude 6.7 and dozens of aftershocks were recorded by ten REFTEK broad-band seismographs in the range of the array of seismograph stations deployed north and south of the Qilian Mountains in April 2003. These records provide nｅw data for the study of the deep structures on the northern Qinghai-Tibetan Plateau. The focus location and focal mechanism study of the shocks of magnitudes >3 show ｔｈａｔ thｏｓｅ earthquakeｓ ｗｅｒｅ initiated by the Jun Ul Mountain thrust fault in the eastern segment of the northern Qaidam basin sinistral strike-slip fault under north-east compression and ａｒｅ the result of continent-continent collision and intracontinental subduction.The strike-slip fault on the northern margin of the Qinghai-Tibet Plateau dips gently in the shallow levels of the earth′s crust, while in the deep levels it usually dips steeply toward the interior. The structure analysis of the hypocenter area verified the influence of the super-deep subduction of the Indian lithospheric plate on the northern margin of the plateau. The nearly east-west displacement of the strike-slip fault formed by the action of north-south stress is still very intense at present.