Sun Daoyuan, Tan Eh, Helmberger Don, Gurnis Michael
Seismological Laboratory, 252-21, California Institute of Technology, Pasadena, CA 91125, USA.
Proc Natl Acad Sci U S A. 2007 May 29;104(22):9151-5. doi: 10.1073/pnas.0608160104. Epub 2007 Apr 10.
Recently, a metastable thermal-chemical convection model was proposed to explain the African Superplume. Its bulk tabular shape remains relatively stable while its interior undergoes significant stirring with low-velocity conduits along its edges and down-welling near the middle. Here, we perform a mapping of chemistry and temperature into P and S velocity variations and replace a seismically derived structure with this hybrid model. Synthetic seismogram sections generated for this 2D model are then compared directly with corresponding seismic observations of P (P, P(C)P, and PKP) and S (S, S(C)S, and SKS) phases. These results explain the anticorrelation between the bulk velocity and shear velocity and the sharpness and level of SKS travel time delays. In addition, we present evidence for the existence of a D" triplication (a putative phase change) beneath the down-welling structure.
最近，有人提出了一个亚稳态热化学对流模型来解释非洲超级地幔柱。它的整体板状形状保持相对稳定，而其内部则经历了显著的搅动，边缘有低速管道，中间附近有下沉流。在这里，我们将化学和温度映射到P波和S波速度变化中，并用这个混合模型取代地震推导的结构。然后，将为这个二维模型生成的合成地震图剖面直接与P波（P、P（C）P和PKP）和S波（S、S（C）S和SKS）相位的相应地震观测结果进行比较。这些结果解释了体波速度与剪切波速度之间的反相关性以及SKS走时延迟的尖锐程度和水平。此外，我们还提供了下沉结构下方存在D”三分相（一种假定的相变）的证据。
