Crustal structure of seismic velocity in southern tibet and east-westward escape of the crustal material
Crustal structure of seismic velocity in southern tibet and east-westward escape of the crustal material
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DOI：
10.1360/03yd0518
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发表时间：
2004-06
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影响因子：
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通讯作者：
Zhongjie Zhang;J. Teng;Yingkang Li;S. Klemperer;Li‐Qiang Yang
中科院分区：
文献类型：
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作者：
Zhongjie Zhang;J. Teng;Yingkang Li;S. Klemperer;Li‐Qiang Yang
本文从北谷错至普莫涌错480 km宽角地震剖面的纵横波波场特征中识别出了莫霍面及地壳内其它界面的反射同相轴。然后，将实测走时与正演计算走时进行拟合，解释了藏南地区近东西向剖面下的地壳纵、横波速度和泊松比结构。解释结果表明，地壳厚度在东西方向上变化明显，表现为以定日以西和定结以东为界的三个区域，莫霍面深度西部约71 km，中部约76 km，东部约74 km。在上地壳底部存在一个低速层，深度为20-30 km。其显著特征之一是LVL厚度从西24 km到东6 km急剧减薄。二是地壳内纵横波速度沿着东西方向的变化均表现出准周期变化特征。下地壳的低速（相对于地球仪大陆的平均速度）和三组南北向的活动正断层，可能是伴随着印度板块与欧亚板块碰撞的下地壳物质拆沉、地壳增厚和地壳物质东西向逃逸的耦合作用的结果。
The reflecting events from Moho and other interfaces within the crust are recognized from the wavefield characteristics of P- and S-wave for the 480km long wide-angle seismic profile between Peigu Tso and Pumoyong Tso. Then, seismic crustal structures of P- and S-wave velocities and Poisson ratio under the nearly east-west profile in southern Tibet are interpreted by fitting the observed traveltimes with the calculated ones by forward modelling. Our interpreting results demonstrate that the crustal thickness varies remarkably in the east-west direction, showing a pattern that the crust could be divided into three parts bounded by the west of Dingri and the east of Dinggyê, respectively, where the depth of Moho is about 71km for the western part, about 76km for the middle and about 74km for the eastern. There is one lower velocity layer (LVL) at the bottom of the upper crust with depth of 20–30 km. One of the distinct features is that the thickness of LVL abruptly thins from 24km on the west to 6km on the east. The other is that the velocity variation in the crust along east-west direction for both P- and S-wave displays a feature as quasi-periodic variation. The lower velocity (compared to the average value for the continent of the globe) in the lower crust and three sets of north-southward active normal faults are probably attributed to the coupling process of material delamination in the lower crust, crustal thicking and east-westward escape of the crustal material accompanied with the continental collision between India and Eurasia Plate.