利用Rayleigh波相速度和群速度联合反演青藏高原东北缘S波速度结构

利用青藏高原东北缘地区固定和流动地震台网2007年8月到2012年1月期间记录的远震波形，运用小波变换频时分析方法分别测定了1216和653条周期从15到140 s的台站间基阶Rayleigh相速度和群速度频散曲线.通过对上述频散进行反演，重构了青藏高原东北缘分辨率高达0.5°×0.5°的2-D相速度和群速度分布图.然后通过对所提取到的每个格网点Rayleigh波相速度和群速度频散进行联合反演，得到了研究区下方一维S波速度结构.最后通过线性插值，得到了青藏高原东北缘下方地壳上地幔三维S波结构.结果表明，印度板块向北俯冲已经达到班公-怒江缝合带附近；在柴达木盆地北部祁连山下面我们发现了亚洲板块，且其没有表现出明显的向南俯冲的迹象；在两大板块中间，我们观测到延伸到250 km深度的低速异常，该低速异常可能是地幔物质底辟上涌现象造成的.

S-wave velocity structure of the northeastern Tibetan Plateau from joint inversion of Rayleigh wave phase and group velocities

The teleseismic waveforms recorded by permanent and temporary networks in NE Tibet from Aug. 2007 to Jan. 2012 have been used to obtain the fundamental mode Rayleigh-wave dispersion data. The Rayleigh wave phase and group velocities along 1216 and 653 paths respectively, were estimated by the wavelet transformation method. These dispersion data were utilized to construct 2-D phase and group velocity maps for the period range 15~140 s. The tests show that the horizontal resolution across the region is about 0.5° for the periods used in this study. The Rayleigh wave phase and group velocity dispersions at each 0.5° cell were jointly inverted to determine 1-D shear wave velocity structure and then assembled into 3-D model by simple linear method. The results show that the Indian plate is preserved till it gets subducted beneath Bangong-Nujiang suture zone. The Asian plate is imaged beneath north of Qaidam basin and Qilian mountain, and does not show obvious sign of southward underthrusting. Between the two plates, a low velocity anomaly extends from the top of upper mantle down to 250 km, which may be caused by the mantle delamination.