The first three-dimensional (3-D) P and S wave attenuation (Qp and Qs) tomography of the crust and upper mantle of the northern Sumatra subduction zone is determined. We adopt an improved calculation scheme to precisely measure attenuation factor t* values from velocity amplitude spectral ratios among different stations that recorded the same earthquake. Our tomographic results show that the forearc accretionary wedge in Sumatra exhibits a significant high-attenuation (low-Q) zone along the trench. The seismic attenuation characteristics of the forearc accretionary wedge are probably influenced by variations in temperature and water content. The middle and upper crust beneath active arc volcanoes shows low-Q and high-Qp/Qs, while the lower crust exhibits less low-Q and low-Qp/Qs, probably reflecting hot volcanic roots with different water saturations from the upper to lower crust. Beneath the Toba volcano that had a super-eruption ∼74,000 years ago, a distinct low-Qp/Qs zone is revealed, which may reflect a transport pathway of fluids and/or local melts ascending from a slab window. The subducting Indo-Australian slab beneath the forearc island chain exhibits a low-Q and low-Qp/Qs belt, reflecting a moderate water saturation probably associated with backthrust faulting. High-Q and high-Qp/Qs zones appear along the slab surface, reflecting large amounts of fluids releasing from the slab dehydration, which may increase pore pressure and cause intense intraslab seismicity.

中文翻译：

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北苏门答腊的增生楔、弧岩浆作用和流体迁移：来自地震衰减断层扫描的见解


确定了北苏门答腊俯冲带地壳和上地幔的第一次三维 （3-D） P 和 S 波衰减 （Qp 和 Qs） 断层扫描。我们采用改进的计算方案来精确测量记录同一地震的不同台站之间的速度振幅谱比的衰减系数 t* 值。我们的层析结果表明，苏门答腊的前弧增生楔沿海沟表现出明显的高衰减 （low-Q） 区。前弧增生楔的地震衰减特性可能受温度和含水量变化的影响。活弧火山下方的中上地壳表现出低 Q 和高 Qp/Qs，而下地壳表现出较少的低 Q 和低 Qp/Qs，可能反映了热火山根，从上地壳到下地壳具有不同的水分饱和度。在大约 74,000 年前发生过超级喷发的多巴火山下方，揭示了一个明显的低 Qp/Qs 区，这可能反映了流体和/或从板窗上升的局部熔体的运输路径。前弧岛链下方的俯冲印度-澳大利亚板块呈现出低 Q 和低 Qp/Qs 带，反映了可能与逆冲断层有关的适度水饱和度。高 Q 和高 Qp/Qs 区域沿板表面出现，反映了板脱水释放的大量流体，这可能会增加孔隙压力并导致板内强烈的地震。