摘要
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50～55km、柴达木块体和河西走廊为45km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VP/VS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VP／VS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45～55km厚的地壳可能主要是通过上地壳的叠置形成的．
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 VP/VS 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 VP/VS value inferred from the grid-search method. Our results show that the crust is 50 - 55kin thick beneath Qilian terrane, and about 45 km beneath the Hexi corridor and Qaidam terrane. The VP/VS 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 VP/VS 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.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2006年第5期1359-1368,共10页
Chinese Journal of Geophysics
基金
国家自然科学基金(40274029
40574040)
地震科学联合基金项目(105096)资助
关键词
青藏高原东北缘
接收函数
地壳结构
泊松比
The NE Tibetan Plateau, Receiver functions, Crustal structure, Poisson ratio
