青藏高原东北缘地壳S波速度结构与泊松比及其意义

利用甘肃地震台网16个台站记录的远震资料，采用最大熵谱反褶积方法，得到了各个台站的接收函数. 采用接收函数扫描法和线性反演方法对研究区的壳幔结构进行了研究，这两种接收函数方法得出的结果具有很好的一致性. 青藏高原东北缘地壳厚度变化剧烈，祁连块体为50～55 km、柴达木块体和河西走廊为45 km左右（合作台除外），由北向南，Moho界面呈中央下凹的准对称状. 研究区地壳VP/VS介于1.66～1.85（σ=0.215～0.294，均值0.254），其均值接近或略低于全球平均值；S波速度结构可见壳幔过渡带具有明显的突跳，结合其他地球物理学证据，推断该区可能不存在岩浆底侵作用和地壳部分熔融现象. 该区地壳VP/VS值与地壳厚度呈反相关关系，推断该区地壳的主要组成成分以中酸性岩石为主，其45～55 km厚的地壳可能主要是通过上地壳的叠置形成的.

The Poisson ratio and crustal structure across the NE Tibetan Plateau determined from receiver functions

We selected broadband teleseismic waveform data recorded by the Gansu Digital Seismic Network to study the crustal and upper mantle structure beneath the Northeastern Tibetan Plateau. The crustal thickness and VP/VS ratio are estimated by the grid_search method using crustal conversion and multiples, assuming an average P_wave velocity in the crust. Teleseismic P waveform modeling is carried out to investigate the S_wave velocity structure, assuming the fixed VP/VS value inferred from the grid_search method. Our results show that the crust is 50～55km thick beneath Qilian terrane, and about 45 km beneath the Hexi corridor and Qaidam terrane. The VP/VS ranges from 166～185, and the Poisson's ratio is about 0215～0294 Our results also show that the Moho interface is sharp beneath the Northeastern Tibetan Plateau. Both of the low_to_normal Poisson's ratio and the sharp Moho don't support the argument of significant partial melting in the upper_to_middle crust and underplating beneath the lower crust of the Northeastern Tibet Plateau. The existence of anticorrelation between VP/VS and the crustal thickness strongly suggests that the crust is mainly composed of felsic mineral in the northeastern Tibetan crust. The seismic evidence may indicate that the thickened crust, mostly in its upper part, is probably due to successive intracrustal thrusts.