Three-dimensional structure of the African superplume from waveform modelling
Three-dimensional structure of the African superplume from waveform modelling
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DOI：
10.1111/j.1365-246x.2005.02508.x
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发表时间：
2005-05
影响因子：
2.8
通讯作者：
S. Ni;D. Helmberger;J. Tromp
中科院分区：
文献类型：
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作者：
S. Ni;D. Helmberger;J. Tromp
以前对地震波形和走时的二维建模显示，非洲地下存在大规模的脊状速度异常，通常称为非洲超级羽流。该构造起自南印度洋，向西北延伸进入大西洋，其基底位于核幔边界。该构造具有相对尖锐的横向边界，内部剪切速度比周围地幔低3%，而压缩速度几乎正常。南非地震台阵记录的西太平洋地震波形最好地说明了三维结构。衍射的S相位沿结构的轴沿着行进超过60°，其中北方和最南方的路径对其边缘进行采样。S波形是简单的，但是对于采样结构中间的路径延迟高达20 s，而对于沿沿着边界的路径，它们显示两个到达。这些复杂的波形可以解释为三维多路径，由于剪切波速度的快速横向变化沿着边缘的结构。这些尖锐的功能，确认与拟议的脊结构与两个独立的方法：谱元素法和基于射线的3-D代码（DWKM）的宽带记录建模。
SUMMARY Previous 2-D modelling of seismic waveforms and traveltimes has revealed a large-scale ridge-like velocity anomaly beneath Africa, which is usually referred to as the African superplume. The structure starts from the southern Indian Ocean and extends northwestwards into the Atlantic Ocean, with its base on the core–mantle boundary. The structure has relatively sharp lateral boundaries with the shear velocity inside 3 per cent lower than the ambient mantle, while the compressional velocity is almost normal. The 3-D structure is best illustrated by seismic waveforms recorded by the South Africa Array generated by earthquakes in the western Pacific Ocean. The diffracted S phase travels along the axis of the structure for over 60°, with the northern- and southernmost paths sampling its edges. The S waveforms are simple but delayed by up to 20 s for paths sampling the middle of the structure, whereas they display two arrivals for paths along the boundaries. These complex waveforms can be explained by 3-D multipathing due to rapid lateral variations in shear-wave velocity along the edges of the structure. These sharp features are confirmed by modelling broadband records associated with the proposed ridge structure with two independent methods: the spectral element method and a ray-based 3-D code (DWKM).