Surveying fault structures by geophysical exploration technique on the northwestern margin of Xining basin

The temporal-spatial distribution characteristics of fault structures on the northwestern margin of Xining basin were investiga-ted by using the audio-magnetotelluric method and 2D seismic exploration,with the purpose of providing the hydrogeological borehole properly so as to carry out the comprehensive investigation and evaluation of hydrogeology,environmental geology and engineering geolo-gy in eastern cities of Qinghai Province,find out the stratigraphic structures and geological structures,and study geophysical characteris-tic parameters in the key region.The results show clearly that there exists Xiamen thrusting-nappe fault on the northwestern margin of Xining basin,which dips NW,with dip angle about 65°.The other two fractures were found in the river valley,away from mountains,and both are presumably associated with Nanmenxia strike-slip fault.In addition,the response characteristics of stratigraphic lithology,appar-ent resistivity and the velocity of seismic reflection wave were summarized.The hydrogeological borehole was drilled to verify the exist-ence of Xiamen thrusting-nappe fault.The drilling coring is quite consistent with the results from the geophysical exploration methods. Several fault fracture zones exist in this borehole penetrating the Neo-Proterozoic crystalline limestone.