Seismic anisotropy in the Sumatra subduction zone
Seismic anisotropy in the Sumatra subduction zone
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DOI：
10.1002/jgrb.50157
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发表时间：
2013-10-01
影响因子：
3.9
通讯作者：
Natawidjaja, D.
中科院分区：
文献类型：
--
作者：
Collings, R.;Rietbrock, A.;Natawidjaja, D.
通过横波分裂（SWS）观测测量地震各向异性是了解俯冲带内发生变形的一个重要工具。在苏门答腊岛，2007年12月至2009年2月期间部署了两个临时地震台网，覆盖了弧前岛屿与弧后岛屿之间的前弧。我们使用SKS和局部SWS测量来确定各向异性的类型、数量和位置。弧前岛屿的局部SWS测量显示出与海沟平行的快速方向，这可归因于上覆沉积物中裂缝/裂缝的形状优选方向。在苏门答腊断裂带，主要的快速方向是断/沟平行，而在弧后地区，主要的快速方向是沟垂直。在地幔楔中，沟垂直方向的延迟时间与射线路径长度呈正相关，而断层平行方向的测量结果与在苏门答腊断层两次地壳事件中观测到的断层平行快速方向相似。这表明存在两层各向异性：一层是由地幔楔内部的夹带流动引起的，第二层是由苏门答腊断层引起的剪切应变引起的覆盖地壳内部的各向异性。SKS分裂结果显示NNW-SSE快速方向，延迟时间为0.8 ~ 3.0s。快速方向近似平行于俯冲的印度-澳大利亚板块的绝对板块运动。局部SWS表现出较小的延迟时间（0.05 ~ 0.45s），结合SKS的大延迟时间，表明产生远震SWS的各向异性主要是板下软流层的夹带流。
An important tool for understanding deformation occurring within a subduction zone is the measurement of seismic anisotropy through observations of shear wave splitting (SWS). In Sumatra, two temporary seismic networks were deployed between December 2007 and February 2009, covering the fore arc between the fore-arc islands to the back arc. We use SKS and local SWS measurements to determine the type, amount, and location of anisotropy. Local SWS measurements from the fore-arc islands exhibit trench-parallel fast directions which can be attributed to shape preferred orientation of cracks/fractures in the overriding sediments. In the Sumatran Fault region, the predominant fast direction is fault/trench parallel, while in the back-arc region it is trench perpendicular. The trench-perpendicular measurements exhibit a positive correlation between delay time and raypath length in the mantle wedge, while the fault-parallel measurements are similar to the fault-parallel fast directions observed for two crustal events at the Sumatran Fault. This suggests that there are two layers of anisotropy: one due to entrained flow within the mantle wedge and a second layer within the overriding crust due to the shear strain caused by the Sumatran Fault. SKS splitting results show a NNW-SSE fast direction with delay times of 0.8-3.0s. The fast directions are approximately parallel to the absolute plate motion of the subducting Indo-Australian Plate. The small delay times exhibited by the local SWS (0.05-0.45s), in combination with the large SKS delay times, suggest that the anisotropy generating the teleseismic SWS is dominated by entrained flow in the asthenosphere below the slab.