Seismic Anisotropy in the Uppermost Mantle beneath the Northeastern Margin of Qinghai-Tibet Plateau: Evidence from Shear Wave Splitting of SKS, PKS and SKKS
详细信息
- 责任者：Wang Qiong (Institute of Earthquake Science ; China Earthquake Administration ; Beijing 100036 ; China) ; Gao Yuan
- 刊名：Chinese Journal of Geophysics
- 出版年：2013
- 卷期：56(3)
- 关键词：上地幔 ; upper mantle ; 各向异性 ; anisotropy ; 横波分裂 ; S-wave splitting ; 青藏高原 ; Qinghai-Tibetan Plateau
- 页码：p.892-905
- 图表：illus., 2 tables, 53 refs.
- 分类号：0400
- issnNo：ISSN0001-5733
- isbnNo：CN11-2074/P
摘要
Based on teleseismic PKS,SKS and SKKS phases(XKS) recorded by 41 permanent broadband stations in Gansu province in northeastern margin of Qinghai-Tibet plateau,this study obtains the splitting parameters of fast polarization direction and delay time between the fast and slow shear waves at each station using the minimum transverse energy method,and then,plots the distribution map of upper mantle anisotropy around this area.Furthermore,combined with GPS velocity field and crustal anisotropy from near-field shear-wave splitting using SAM method,we discuss the characteristics and formation mechanism of the crust-mantle anisotropy in the northeastern margin of Qinghai-Tibet plateau.The results can be summarized as follows.In the west part of Altun fault,the fast wave polarization trends NWW—SEE,siting at a certain degree angle to the strike of regional structures,while coinciding with the subduction direction from Tarim Basin to Qaidam Basin,which reveals that in this region,the upper mantle deformation is mainly affected by ancient tectonic movement so that it belongs to "fossil" anisotropy.In Qilian-Hexi Corridor tectonic region,the XKS fast direction is NW—SE,consistent with strike direction of the main fault in this area.while the fast direction obtained from near-field shear-wave splitting is NE-SW,consistent with GPS velocity relative to stable Eurasian Continent.The different direction between crust and mantle suggests that the deformation mechanism of them may be different in this area.Crust anisotropy represents the direction of regional principal compressive stress,and XKS anisotropy may reflect the direction where materials flow.In Longzhong Basin and adjacent regions,which located in the transition zone between the active Qinghai-Tibet block and comparatively stable Ordos block,with more complex tectonic background,the fast directions in the crust and in the upper mantle are consistent by and large,which means that the crust and the upper mantle possibly have the same deformation,but owing to local feature′s influence,the results vary obviously with these stations.
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