Seismic anisotropy beneath the southern Himalayas‐Tibet collision zone
Seismic anisotropy beneath the southern Himalayas‐Tibet collision zone
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DOI：
10.1029/97jb01424
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发表时间：
1997-08
影响因子：
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通讯作者：
E. Sandvol;J. Ni;R. Kind;Wenjin Zhao
中科院分区：
文献类型：
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作者：
E. Sandvol;J. Ni;R. Kind;Wenjin Zhao
利用国际西藏和喜马拉雅山深地震探测II（INDEPTH-II）台阵在东喜马拉雅和西藏采集的剪切波ScS、SKS和SKKS相，分析了南喜马拉雅-西藏碰撞带下偏振地震各向异性的方向和程度。除了位于印支-藏布缝合带以北约100公里处的两个北方台站外，在碰撞区的这一部分台站没有看到任何剪切波分裂的证据。在缝合线和特提斯喜马拉雅山附近的台站下方缺乏剪切波分裂，表明在碰撞带的这一部分下方没有明显的大规模地幔偏振地震各向异性。缺乏偏振地震各向异性的一个解释是，一个近垂直的地幔剪切应变场所造成的下涌地幔流增厚的印度下大陆岩石圈。在Gandese带以北，分裂剪切波的快速方向是东北-西南方向，大致平行于一个主要的左旋走滑断裂带的趋势，边界的Gulu裂谷。平行于地表地质剪切带的快极化方向与上地壳应变速率场中剪切面方向的一致性表明了岩石圈范围内的相干变形。
Shear wave phases ScS, SKS, and SKKS, collected from the Project International Deep Seismic Sounding of Tibet and Himalayas II (INDEPTH-II) array in the eastern Himalayas and Tibet are analyzed for the orientation and extent of polarization seismic anisotropy beneath the southern Himalayas-Tibet collision zone. No evidence is seen for any shear wave splitting for stations in this part of the collision zone except for two northern stations located about 100 km north of the Indus-Tsangpo Suture. The lack of shear wave splitting beneath the stations in the vicinity of suture and the Tethyan Himalayas indicates that there is no appreciable large-scale mantle polarization seismic anisotropy beneath this part of the collision zone. One explanation for the lack of polarization seismic anisotropy would be a subvertical mantle shear strain field resulting from a downwelling mantle flow of a thickened Indian lower continental lithosphere. North of the Gandese belt, the fast directions of the split shear waves are oriented in a northeast-southwest direction, approximately parallel to the trend of a major left-lateral strike-slip fault zone that bounds the Gulu rift. The coincidence of fast polarization directions parallel to the surficial geologic shear zones and the direction of shear planes within the upper crustal strain rate field suggests lithospheric-wide coherent deformation.