Upper-mantle velocity structures beneath the Tibetan Plateau and surrounding areas inferred from triplicated P waveforms  

作　　者：RiSheng Chu LuPei Zhu ZhiFeng Ding 

机构地区：[1]State Key Laboratory of Geodesy and Earth’s Dynamics,Institute of Geodesy and Geophysics,Wuhan 430077,China [2]Department of Earth and Atmospheric Sciences,Saint Louis University,St Louis,MO 63108,USA [3]Institute of Geophysics and Geomatics,China University of Geosciences,Wuhan 430074,China [4]Institute of Geophysics,China Earthquake Administration,Beijing 100083,China

出　　处：《Earth and Planetary Physics》2019年第5期444-458,共15页地球与行星物理（英文版）

基　　金：supported by funding from the Strategic Priority Research Program(B)of Chinese Academy of Sciences through grant XDB18010304;Natural Science Foundation of China through grant 41322027,41374060,41374079,41661164035

摘　　要：P-wave waveforms in the distance range between 12°and 30°were analyzed to investigate upper-mantle P velocity structures beneath the Tibetan Plateau and surrounding areas.The waveform data from 504 earthquakes with magnitudes larger than 5.0 between 1990 and 2005 that occurred within 30°from the center of the Plateau were modelled.We divided the study area into 6 regions and modeled upper-mantle-distance P waveforms with turning points beneath each region separately.The results show that the uppermantle P-wave velocity structures beneath India,the Himalayas,and the Lhasa Terrane are similar and contain a high-velocity lid about 250 km thick.The upper-mantle velocities down to 200 km beneath the Qiangtang Terrane,the Tarim Basin,and especially the Songpan-GarzêTerrane are lower than those in the south.The 410-km discontinuity beneath these two terranes is elevated by about 20 km.Highvelocity anomalies are found in the transition zone below 500 km under the Lhasa and Qiangtang Terranes.The results suggest that the Tibetan Plateau was generated by thrusting of the Indian mantle lithosphere under the southern part of Tibet.Portions of the thickened Eurasian mantle lithosphere were delaminated;they are now sitting in the transition zone beneath southern Tibet and atop of the 410-km discontinuity underneath northern Tibet.P-wave waveforms in the distance range between 12° and 30° were analyzed to investigate upper-mantle P velocity structures beneath the Tibetan Plateau and surrounding areas. The waveform data from 504 earthquakes with magnitudes larger than 5.0 between 1990 and 2005 that occurred within 30° from the center of the Plateau were modelled. We divided the study area into 6 regions and modeled upper-mantle-distance P waveforms with turning points beneath each region separately. The results show that the uppermantle P-wave velocity structures beneath India, the Himalayas, and the Lhasa Terrane are similar and contain a high-velocity lid about 250 km thick. The upper-mantle velocities down to 200 km beneath the Qiangtang Terrane, the Tarim Basin, and especially the SongpanGarzê Terrane are lower than those in the south. The 410-km discontinuity beneath these two terranes is elevated by about 20 km. Highvelocity anomalies are found in the transition zone below 500 km under the Lhasa and Qiangtang Terranes. The results suggest that the Tibetan Plateau was generated by thrusting of the Indian mantle lithosphere under the southern part of Tibet. Portions of the thickened Eurasian mantle lithosphere were delaminated; they are now sitting in the transition zone beneath southern Tibet and atop of the 410-km discontinuity underneath northern Tibet.

关 键 词：TIBETAN Plateau upper MANTLE structure triplication waveform modelling 

分 类 号：P[天文地球]