P-wave tomography for 3-D radial and azimuthal anisotropy of Tohoku and Kyushu subduction zones
P-wave tomography for 3-D radial and azimuthal anisotropy of Tohoku and Kyushu subduction zones
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DOI：
10.1093/gji/ggt086
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发表时间：
2013-06
影响因子：
2.8
通讯作者：
Jian Wang;Dapeng Zhao
中科院分区：
文献类型：
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作者：
Jian Wang;Dapeng Zhao
S U M M A R Y我们利用日本列岛密集地震台网记录的大量高质量的地方地震到时数据，确定了东北和九州俯冲带三维径向和方位各向异性的高分辨率P波层析成像。在东北和九州的弧后地幔楔中，均发现了槽向正常的P波快速度方向（FVD），这与板片驱动角流模型相一致。在东北和九州的弧前地幔楔中出现了振幅<4%的沟道平行FVD，表明存在B型橄榄石组构。在东北火山前缘下的地幔楔中也可以看到沟槽平行的FVD，但在九州则没有，这表明东北下的地幔楔中可能存在三维流动，并且三维流动受到海洋板块俯冲速率的影响。东北和九州弧火山下地幔楔的低速带以及九州菲律宾海板块下的低速带显示出负的径向各向异性（即垂直速度快于水平速度），这可能反映了上地幔中存在水时热涌流动和橄榄石组构的转变。在东北俯冲太平洋板块和九州俯冲菲律宾海板块中，发现了平行于海沟的FVD和正的径向各向异性（即水平速度快于垂直速度），表明板块保持了在洋中脊形成的冻结各向异性，或者板块各向异性是由B型橄榄石的晶格择优取向引起的。
S U M M A R Y We determined high-resolution P-wave tomography for 3-D radial and azimuthal anisotropy of the Tohoku and Kyushu subduction zones using a large number of high-quality arrival-time data of local earthquakes recorded by the dense seismic network on the Japan Islands. Trenchnormal P-wave fast-velocity directions (FVDs) are revealed in the backarc mantle wedge in both Tohoku and Kyushu, which are consistent with the model of slab-driven corner flow. Trench-parallel FVDs with amplitude <4 per cent appear in the forearc mantle wedge under Tohoku and Kyushu, suggesting the existence of B-type olivine fabric there. Trench-parallel FVDs are also visible in the mantle wedge under the volcanic front in Tohoku but not in Kyushu, suggesting that 3-D flow may exist in the mantle wedge under Tohoku and the 3-D flow is affected by the subduction rate of the oceanic plate. Negative radial anisotropy (i.e. vertical velocity being faster than horizontal velocity) is revealed in the low-velocity zones in the mantle wedge under the arc volcanoes in Tohoku and Kyushu as well as in the low-velocity zones below the Philippine Sea slab under Kyushu, which may reflect hot upwelling flows and transitions of olivine fabrics with the presence of water in the upper mantle. Trench-parallel FVDs and positive radial anisotropy (i.e. horizontal velocity being faster than vertical velocity) are revealed in the subducting Pacific slab under Tohoku and the Philippine Sea slab under Kyushu, suggesting that the slabs keep their frozen-in anisotropy formed at the mid-ocean ridge or that the slab anisotropy is induced by the lattice-preferred orientation of the B-type olivine.