Azimuthal anisotropy and mantle flow underneath the southeastern Tibetan Plateau and northern Indochina Peninsula revealed by shear wave splitting analyses
Azimuthal anisotropy and mantle flow underneath the southeastern Tibetan Plateau and northern Indochina Peninsula revealed by shear wave splitting analyses
复制标题
DOI：
10.1016/j.tecto.2018.09.013
复制
发表时间：
2018-11-13
期刊：
影响因子：
2.9
通讯作者：
Gao, Stephen S.
中科院分区：
文献类型：
--
作者：
Kong, Fansheng;Wu, Jing;Gao, Stephen S.
利用SKS、SKKS和PIGS震相的分裂方法，对青藏高原东南部与中南半岛过渡区的地震方位各向异性进行了定量研究。在具有一个或多个分裂测量的50个台站中，22个台站具有足以识别和表征复杂各向异性的方位角覆盖范围。由此产生的分裂参数从15个这样的站表现出系统的背方位角的变化与90度的周期性，这是符合一个两层各向异性模型。上层参数与基于莫霍面P-S转换的正弦时差独立获得的地壳各向异性测量结果一致，快速方向大多平行于主要剪切带。低层快方位和分裂参数方位不变的台站快方位多为E-W向，这与该区主要构造组构地表表现的以N-S向为主的趋势有明显差异。它们也与板块运动的绝对方向不一致。当结合地震层析成像和震源机制解的结果，所观察到的方位各向异性可以充分解释的岩石圈相对于下层软流圈的运动，最有可能与向西回滚的俯冲印度板块。
Seismic azimuthal anisotropy beneath the transitional region between the southeastern Tibetan Plateau and the Indochina Peninsula, an area in which the fast orientation of mantle anisotropy changes to dominantly E-W from mostly N-S on the plateau at the north, is quantified using splitting of the SKS, SKKS, and PIGS phases. Among the 50 stations with one or more splitting measurements, 22 possess an azimuthal coverage that is adequate for the identification and characterization of complex anisotropy. The resulting splitting parameters from 15 such stations exhibit systematic back azimuthal variations with a 90 degrees periodicity, which is consistent with a two-layered anisotropy model. The upper layer parameters are consistent with crustal anisotropy measurements obtained independently based on the sinusoidal moveout of P-to-S conversions from the Moho, with the fast orientations being mostly parallel to major shear zones. The lower layer fast orientations and the fast orientations at stations with azimuthally invariant splitting parameters are mostly E-W, which is significantly different from the dominantly N-S trend of the surface expression of major structural fabrics in the area. They are also inconsistent with the absolute plate motion directions. When combined with results from seismic tomography and focal mechanism solutions, the observed azimuthal anisotropy can be adequately explained by the movement of the lithosphere relative to the underlain asthenosphere, most likely associated with the westward rollback of the subducted Indian Plate.