华北太行山区地壳各向异性的接收函数证据

Crust anisotropy of Taihangshan mountain range in north China inferred from receiver functions

采用具有任意方向对称轴的横向各向同性介质系统,探讨了各向异性介质中接收函数表现出的横波分裂、能量偏离等特征,并系统剖析了各向异性介质对称轴方位角、倾角以及各向异性层位分布对接收函数方位变化花样的影响.太行山隆起地区是研究华北克拉通构造运动以及动力学过程的重要场所.我们以该地区JJJX台为例,介绍了利用远场接收函数研究台站下方地壳各向异性特征的方法.反演结果表明,该台站下方存在明显的来源于中、上地壳的各向异性,浅层2.4km以内表现出强度约为10%的裂隙成因的慢轴型各向异性,裂隙面沿NNE方向展布,与该地区断层走向一致;中地壳表现出强度约为8%的晶体成因的快轴型各向异性,太行山新生代的隆起是形成晶体优势排列方向的一种可能的动力机制.

We investigated the receiver functions in a horizontally-layered medium with arbitrary oriented hexagonally symmetric anisotropy, and discussed the phenomenon of shear-wave splitting and energy deviation in an anisotropic medium. The anisotropic structure yields patterns of receiver function amplitudes and arrival times on both the radial and transverse components that are a systematic function of source-receiver back azimuth. We also investigated the influence of varying anisotropy parameters, e. g. trend and plunge of the symmetry axis, and depth distribution of anisotropy, on the variation pattern. We applied the method of receiver function with anisotropy to one station-JJJX, which is located in the Taihangshan Mountain Range （TMR） of North China. Our results show that the upper crust （0-2.4 km） has about 10% anisotropy with a slow symmetry axis, which might be caused by aligned microcraeks. The trend direction of the symmetry axis has a good correlation with the faults distributed in this area. With a fast symmetry axis, the middle crust （2.4-22 km） has about 8% anisotropy associated with aligned crystals, which might be a result of the uplifting of the TMR occurred in Cenozoic.