[Jiang Li-Jun] Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China
; [Jiang Li-Jun] China Univ Geosci, Inst Geophys & Geomat, Beijing 100083, Peoples R China
; [Li Yong-Hua
; Wu Qing-Ju] China Earthquake Adm, Inst Geophys, Beijing 100081, Peoples R China
Seismic anisotropy beneath the Central Tien Shan is investigated using shear-wave splitting of SKS and SKKS phases. We analyzed teleseismic events recorded by 37 broadband stations in the Central Tien Shan and its vicinity. Fast polarization directions (phi) and delay times (delta t) are determined with both the minimum energy method and rotation-correlation method. Our results suggest that the fast polarization direction of most stations in this area is NEE-SWW, parallel to the strike of the Tien Shan, the delay time is about 0.4 similar to 1.7 s. All of these are exactly the direct reflection of the NS shortening deformation of the lithosphere mantle beneath this area, which is related to the double subduction of Tarim and Kazakhstan. At some stations in the northern part of Central Tien Shan the splitting parameters vary with event back azimuth regularly, which implies that the actual upper-mantle structure is more complex than a single anisotropic layer with horizontal fast axis. The strong transverse variety of the shear wave fast polarizations and delay times of the stations in the west of 75 degrees E maybe related to the small-scale convection beneath this region. The obvious differences of anisotropy between different parts of the Tien Shan verify the complexity of the lithosphere deformation beneath this region.