1206 (Chinese J. Geophys. ) 48 a high resistivity layer in the upper crust, a lower resistivity layer in the top of the lower crust, and the resistivi

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1 CHINESE JOURNAL OF GEOPHYSICS Vol. 48, No. 5 Sep., 2005,,..,2005,48 (5) : Tang J, Zhan Y, Zhao G Z, et al. Electrical conductivity structure of the crust and upper mantle in the northeastern margin of the Qinghai2 Tibet plateau along the profile Maq n2lanzhou2jingbian. Chinese J. Geophys. (in Chinese), 2005,48 (5) : , 1, 1, 1, 1, 2, 3, 1 1, , , , Robust.. RRI, : (1) 4 :. (2) :,,. 3,. (3) ;.,,, (2005) P , Electrical conductivity structure of the crust and upper mantle in the northeastern margin of the Qinghai- Tibet plateau along the profile Maq n2lanzhou2jingbian TANGJi 1, ZHAN Yan 1, ZHAO Guo2Ze 1, DENG Qian2Hui 1, WANGJi2Jun 1, CHEN Xiao2Bin 2, ZHAO Jun2Meng 3, XUAN Fei 1 1 Institute of Geology, China Earthquake Administration, Beijing , China 2 Department of Geophysics, Peking University, Beijing , China 3 Institute of Tibetan Research, Chinese Academy of Sciences, Beijing 10085, China Abstract Magnetotelluric (MT) measurements have been carried out at 62 sites in the junction area between the northeastern margin of the Qinghai2Tibet plateau and the Ordos block along the profile Maq n2lanzhou2 Jingbian. The Robust data processing technique and Bahr s tensor decomposition were used to remove 32D effect. Apparent resistivity, impedence phase curves, skewness and regional strike were analysed. RRI 22D inversion has been used for data interpretation. The results are as follows. (1) The target area can be divided into four electrical conductivity blocks by 3 fault zones named Maq n, Lanzhou and Majiatan2Dashuikeng fault zone. The four blocks are named Bayan Har block, Qinling-Qilian block, margin belt and Ordos block, respectively. (2) The electrical conductivity structure in block 1, 2 and 4 has similar characteristics. There is 973 ( G : ).,,1963,,, E2mail ac. cn

2 1206 (Chinese J. Geophys. ) 48 a high resistivity layer in the upper crust, a lower resistivity layer in the top of the lower crust, and the resistivity rises gradually from the lower crust to the upper mantle. The characteristic of electrical conductivity layer is not well and is complex in the structure in block 3 which is very active in tectonics. (3) The Maq n fault belt, the Haiyuan fault belt and the Luoshan2Yunwushan fault belt extend through the crust with high dip angles and the fault on the northern brim of the Qinling mountains is confined inside the crust. Keywords Magnetotelluric ( MT) survey, Maq n2lanzhou2jingbian, Electrical conductivity structure, Inversion 1, [1 12 ]., ( ) (10, [2,7,8, ]., [17 20 ]., [19 ].,, [12,15, 19,21 ], [18 22 ] ,, 10 ( / ) [18 ] [16,20 ],.,,.,,, , 1000km, ( 1)., ( ), km), (15 40 km),, 5 8 km , 62. Metronix MMS203E GMS05, s., ;, 20h. Metronix PROCMT,,, Robust., Bahr [23 ] ,., [21 ],, A01 A05 A06 A21 A22 A55 A56 A ( ) ( <),, 4.

3 5 : ( [21 ]) Fig. 1 Distribution of MT sites and active blocks in the northeastern margin of the Qinghai2Tibetan plateau (Active block distribution is after Zhang et al. [21 ] ). 2 Fig. 2 Apparent resistivity and impedance phase curves of typical sites

4 1208 (Chinese J. Geophys. ) Bahr [23 ],,,,. 3 ( S).,, 013,., [6 ] ( 1). (Swift ) 30 60, 90,, Bahr [23 ],, Swift,. 4.,. 3,,.,., ( ), TM, TE. (RRI) [24 26 ]. [24,27,28 ],TE,TM, TE + TM.,, TE + TM, TE TM 4, ( TE TM ),,,. TE TM 2 ( 5C)., 6 %, 10 %. 5A 5B TE TM.,,. ( 5C). 4 ( 5) ( 2),, ( 6), [22 ].,,., [29 ]. 411, ( ) ( ) ( ) ( ), (F1) ( F3) (F9) ( ) (A01 A05)., 2 A02,..,. 15km,,.,,,, ;,,, 20 60km,, ; INDEPTH

5 5 : (a) Swift ; (b) Bahr. Fig. 3 Two2dimensional skewness along the profile (a) Switf Skewness ; (b) Bahr Skewness. 4 A r Fig. 4 Primary axes of electrical conductivity of some sites

6 1210 地球物理学报 ( Chinese J. Geophys. ) 48 卷

7 5 : 1211

8 1212 (Chinese J. Geophys. ) 48 [30,31 ].,, 242mWΠm 2[32 ].,,. [33 ].,., ( ) (A06 A21),,,, 2 A06, 4, A13 A18.., (F2),,.,,,,,, 2 km ;.,, ( F2),.., 13km. F2,, 20km.,, I. [18 ],,, ;,,.,., 50 km,,, 60mWΠm 2 [34 ],,,., ( ) (A22 A55). 3,, km,,. [17,19 ], (F4) (F5) (F8) (F9) ( ). [ 13 ]. 4,.. 1 :A22 A26, ;,, ( )., 1s, ( 2 A23 )., 2 km, km, km., [34 ],.. 2 :A27 A33, ;,,., 4 Hz, ( 21 A28 ). 6, ,1920 ( M S = 816) 17km,, [19 ]. 3 : A33 A49,,,

9 5 : 1213., 011 Hz ( 2 A38 ),. 6,,,. 613km, 2 [35 ]. ( ). 4 : A49 A55, ;., ( 2 A53 ),,., [35 ] ( ) (A58 ) :,, 1s,, 100s,,. ( 6),, 20km,,,,, 3km, 2km., [13 ].,.,, [29 ],., C4 ( ) [22 ].,, 4000s,,. 412,,,., MT 5 km, (8 15 km),, ( ) ( 6). (F1) :, A05 ( ),,,.,,. ( F2) : A13 A14,,,,.. ( F3) :, A21,,,.,. (F4) :A24 A25,,,,,.,. ( F5) :A33 A34,,, ( M s 816),, - [19 ],. ( F6) : A44 A45,,,,. ( F7) : A46 A47,,,.,

10 1214 (Chinese J. Geophys. ) 48. ( F8) : A50 A51, A50,,., [19 ]. ( F9) : A57,, 4 km,,,,,, -., km,, : (l),,.,.,. (2),,, ;,,,, [29 ] ; 3,,,,, [29 ].,,,. [22 ],. (3),,,,,, [32 ] ;,,,, [29 ] ;,,,. (4),., ( 6),.,. (5),,,,,. ( ),, ( )., H., km, 1 3, 2 4.,,, INDEPTH 2 4, 2 [15 ] ; (Network2MT) [15,16 ],, GDS,,,.,. GS(2005) 670. (References) [ 1 ]..,1995,1 :1 9 Li Y D. Uplifting process and mechanism of Qinghai2Tibet plateau. Acta Geoscientia Sinica (in Chinese), 1995, 1 : 1 9 [ 2 ] Molnar P, Tapponnier P. Cenozoic tectonics of Asia : effects of a continental collision. Sicence, 1975, 189 : [ 3 ],,.. :.. :,

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14 17.,., Fig. 1 Bougeur gravity map of research region 2 Fig. 2 Magnetic map of research region

14 17.,., Fig. 1 Bougeur gravity map of research region 2 Fig. 2 Magnetic map of research region 1 7 1 Vol. 17 No. 1 2002 3 (13 23) PROGRESS IN GEOPHYSICS March 2002 (,,100101) [ ],, 39.,,. [ ] ; ; [] P738 [] A [ ]100422903 (2002) 0120013211 0,,.,,, NE [1 ],.., ( NE, EW,NE ),.,.,,. 1 20 20 km ( 10