Crustal origin of trench-parallel shear-wave fast polarizations in the Central Andes
Crustal origin of trench-parallel shear-wave fast polarizations in the Central Andes
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DOI：
10.1016/j.epsl.2014.02.032
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发表时间：
2014-04
影响因子：
5.3
通讯作者：
I. Wölbern;U. Löbl;G. Rümpker
中科院分区：
文献类型：
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作者：
I. Wölbern;U. Löbl;G. Rümpker
在这项研究中，分析了SKS和当地的S震相，以研究横跨安第斯高原中部和普纳高原的两条密集地震剖面上横波分裂参数的变化。与以前的观测结果不同，绝大多数测量结果显示快偏振次平行于纳斯卡板块俯冲方向，延迟时间在0.3%至1.2%S之间。局部相显示出较大的快偏振变化，延迟时间在0.1%至1.1%S之间。沿阿尔蒂普诺剖面的两个70公里和100公里宽的剖面显示出较大的延迟时间，其特征是快速极化方向次平行于主要断裂带。基于各向异性俯冲带模型的有限差分波场计算，我们证明，快速对称轴与板块运动次平行的化石板块各向异性，以及近沟平行快轴取向的地壳各向异性的重要分量，可以很好地解释观测结果。由于快速极化的短尺度变化，我们从模拟中排除了观测到的强异常的亚岩石圈起源。相反，我们的结果表明，中央安第斯山脉的各向异性通常反映了板块运动的方向，而观测到的沟槽平行的快速极化可能起源于俯冲板块上方的大陆地壳。
In this study, SKS and local S phases are analyzed to investigate variations of shear-wave splitting parameters along two dense seismic profiles across the central Andean Altiplano and Puna plateaus. In contrast to previous observations, the vast majority of the measurements reveal fast polarizations sub-parallel to the subduction direction of the Nazca plate with delay times between 0.3 and 1.2 s. Local phases show larger variations of fast polarizations and exhibit delay times ranging between 0.1 and 1.1 s. Two 70 km and 100 km wide sections along the Altiplano profile exhibit larger delay times and are characterized by fast polarizations oriented sub-parallel to major fault zones. Based on finite-difference wavefield calculations for anisotropic subduction zone models we demonstrate that the observations are best explained by fossil slab anisotropy with fast symmetry axes oriented sub-parallel to the slab movement in combination with a significant component of crustal anisotropy of nearly trench-parallel fast-axis orientation. From the modeling we exclude a sub-lithospheric origin of the observed strong anomalies due to the short-scale variations of the fast polarizations. Instead, our results indicate that anisotropy in the Central Andes generally reflects the direction of plate motion while the observed trench-parallel fast polarizations likely originate in the continental crust above the subducting slab.