P wave anisotropic tomography of the Nankai subduction zone in Southwest Japan
P wave anisotropic tomography of the Nankai subduction zone in Southwest Japan
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DOI：
10.1029/2012gc004081
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发表时间：
2012-05
期刊：
影响因子：
3.7
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
年轻菲律宾海（PHS）板块和老太平洋板块的活跃俯冲导致日本西南部（SW）地区出现显着的地震不均匀性和各向异性。在这项工作中，我们使用 1095 个台站记录的 5,249 次当地地震的约 540,000 个 P 波到达时间，确定了日本西南部地壳和上地幔的详细 3D P 波各向异性层析成像。 PHS 板片清晰地成像为高速（高 V）异常，表现出相当大的横向变化。 PHS 板的上方和下方显示出显着的低速 (low-V) 异常。 PHS板片上方的低V异常可能反映了地幔楔的上升流和PHS板片的脱水作用，它们形成了日本西南部弧火山的源区。 PHS板片下方的低V区可能反映了太平洋板片上方大地幔楔的上升流。地壳和上地幔的各向异性是复杂的。在九州地区，弧后地幔楔内的P波快速度方向（FVD）总体呈海沟法向，这与PHS板片俯冲驱动的角流一致。 FVD 在九州之下的俯冲 PHS 板片中与海沟平行。我们认为板内地震活动是板各向异性的潜在指标。也就是说，具有地震活动性的PHS板片保留了其在洋中脊形成的原始化石各向异性，而抗震PHS板片则根据其当前的变形再现了各向异性。
The active subduction of the young Philippine Sea (PHS) plate and the old Pacific plate has resulted in significant seismic heterogeneity and anisotropy in Southwest (SW) Japan. In this work we determined a detailed 3‐D P wave anisotropic tomography of the crust and upper mantle beneath SW Japan using ∼540,000 P wave arrival times from 5,249 local earthquakes recorded by 1095 stations. The PHS slab is imaged clearly as a high‐velocity (high‐V) anomaly which exhibits considerable lateral variations. Significant low‐velocity (low‐V) anomalies are revealed above and below the PHS slab. The low‐V anomalies above the PHS slab may reflect the upwelling flow in the mantle wedge and the PHS slab dehydration, and they form the source zone of the arc volcanoes in SW Japan. The low‐V zones under the PHS slab may reflect the upwelling flow in the big mantle wedge above the Pacific slab. The anisotropy in the crust and upper mantle is complex. In Kyushu, the P wave fast velocity direction (FVD) is generally trench‐normal in the mantle wedge under the back‐arc, which is consistent with the corner flow driven by the PHS slab subduction. The FVD is trench‐parallel in the subducting PHS slab under Kyushu. We think that the intraslab seismicity is a potential indicator to the slab anisotropy. That is, the PHS slab with seismicity has kept its original fossil anisotropy formed at the mid‐ocean ridge, while the aseismic PHS slab has reproduced the anisotropy according to its current deformation.