In this study, we conducted seismic tomographic inversions to investigate the velocity and anisotropy structures of northern Sumatra, using 9774 P-wave and 8405 S-wave arrivals from regional earthquakes. Isotropic P-wave velocity, isotropic S-wave velocity, P-wave azimuthal anisotropy, and P-wave radial anisotropy models were generated using eikonal equation-based traveltime tomography methods. The study identified low-velocity zones beneath the Toba and Sinabung volcanoes, potentially indicating the presence of magma reservoirs. Furthermore, low-velocity anomalies above the subduction slab were detected, which were likely caused by the dehydration of the slab and interpreted as channels of upwelling flow. The tomographic results revealed a trench-parallel high-velocity belt in the uppermost mantle, representing the subducting slab of the India-Australian plate. The trench-parallel fast velocity directions in the slab suggested that the subducted oceanic slab retains its frozen-in anisotropy formed at the mid-ocean ridge, or that the anisotropy is induced by the lattice-preferred orientation of the B-type olivine. Negative radial anisotropy in the mantle wedge was observed, reflecting hot upwelling flows and transitions of olivine fabrics in the presence of water due to slab dehydration. The results also indicated a multilevel magma plumbing system beneath the Toba Caldera. In summary, the results of this study provided new insights into the structure and dynamic processes of the northern Sumatra subduction zone.

中文翻译：

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对苏门答腊北部俯冲带的速度和各向异性结构的新见解


在这项研究中，我们使用来自区域地震的 9774 个 P 波和 8405 个 S 波到达，进行了地震断层扫描反演，以研究苏门答腊北部的速度和各向异性结构。各向同性 P 波速度、各向同性 S 波速度、P 波方位各向异性和 P 波径向各向异性模型是使用基于艾康方程的传播时间断层扫描方法生成的。该研究确定了多巴火山和锡纳邦火山下方的低速区，这可能表明存在岩浆储层。此外，还检测到俯冲板块上方的低速异常，这可能是由板块脱水引起的，并被解释为上升流的通道。层析结果显示，在最上部的地幔中有一个海沟平行的高速带，代表印度-澳大利亚板块的俯冲板。板块中海沟平行的快速速度方向表明，俯冲洋板块保留了在洋中脊形成的冻结各向异性，或者各向异性是由 B 型橄榄石的晶格优先取向引起的。在地幔楔中观察到负径向各向异性，反映了由于板脱水而在水存在下橄榄石织物的热上升流和过渡。结果还表明，多巴火山口下方存在多层岩浆管道系统。综上所述，本研究结果为苏门答腊北部俯冲带的结构和动态过程提供了新的见解。