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《Chinese Journal of Geophysics》 1997-03
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SHEAR WAVE VELOCITY STRUCTURE IN DABIESHAN OROGENIC BELT

WANG CHLJN-YONGJ;DING ZHI -FENG;SONG JIAN-LI;WU QING-JU;ZHENG JI -CAI;ZHANG XIAO-BINGl1) (Institute of Geophysics, State Seismological Bureau, Beijing 100081 , China)2)(Geophysical Prospecting Cealer, State Seismological Bureau, Zheagzhou 450003, China)  
Based on the 2-D P wave velocity structure from the deep seismic sounding prcrfile across the Dabieshan orogenic belt, the horizontal components of seismic recordswere used to determine the shear wave velocity structure. And then, the data of Pwave and S wave were jointly used to restrain the composition of crust' The phasesSg and SmS appear clearly on the records of most shotpoints, and the converted wavePmS reflected from the Moh0 shows on the records of the Butasi and the Jing0ngshotpoints. lt indicates that the Moho is a first-order disc0ntinuity onthe relevant re-gion. That the record containing both strong Pn and SmS is lacking in the related Snmay indicate that the P0isson ratio in the uPpermost mantle increases shmp1y Withdepth, and the locally melting material may ekist at this dePth' The model of thePoisson ratio in crust dem0nstrates that it is about O'25 at the depth Iess than lOtriin the uPper crust along the whole proflle except the North Huayang Flysch Beltwhere it is O'23, O'26 - O'27 in the lower crust of both the Yangtze block and N0rthChina block, O-22- 0-24 in the lower part of the uPper crust and O'27- 0-3O in thelower crust in the Dabieshan or0genic belt, where it is the highest in the Ultra-HighPressure belt' The P, S velocities and P0isson rati0 j0intly il1ustrate that the basicgranulite is the main c0mp0sition of the l0wer crust in the Ultra-High Pressure belt'The lateral heterogeneity of the composition in the mid~lower crust of the Dabieshanorogenic belt indicates that the Yangtze block subducted to the North Chna block inthe Triassic orogeny, and the magma intrusion related t0 the mantle material mayekist there'
【Fund】: 国家自然科学基金;;地震科学联合基金;;国家地震局资助项目
【CateGory Index】: P542
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