EARTH ELECTROMAGNETIC SOUNDING AT SOUTHWESTERN MARGIN OF EERDUOSI BLOCK

This paper summarises the earth eleotromagnetic sounding results for Qingyiang-Yongqing profile of Gansu Province at southwestern margin of Eerduosi block. This profil-goes across differeat geologic structural elements from Eerduosi block to Qingzang block along E-W direction of 36°north latitude, The sounding results not only reflect the eltcric property in regional crust-uper mantle in each geologic structural elemnt but also show remarkble transverse variation elctric propertyi display the comprersicnal action between Qingzang block and Eerduosi block. The paper also discusses the distribution form of geothermal heat flow along the profile estimated by the earth electromagnetic sounding results, and overviews regional distribution charaeteristics of estimated geothermal heat flow values of 40 observation points along west margin of Eerduesi and nerthern secticn of South-North seismic belt. The high heat flow area distributes from north to cuth like belt and its margin area is obviousl corresponding with seismtcity: the epicentres of 6 great earthquakes with M≥7(1/2) occurred in the recent 3 hundred years in the surveyed area all distributed in margin areas of high heat folw. Therefor, the margin areas of high heat folw value areas can be used as one of criteria for judging a potential great earthquake focal area like "the gradient variation zone on the top of layer of flowagell, especially thiekened high conductive layer incrust" and "sharply transverse variation of electric property in cruit".