Mapping Chemical Plumes from Bottom to Top

在绘制地球横向变化图方面已经取得了相当大的进展，展示了我们下面正在进行的活跃的动态过程。地震层析成像技术在走时和波形方法学方面的进步使得地幔的主要结构得以确定。环太平洋的相对较快的速度来自全球长期研究，并通过更短的波长体波和更高模式的努力进一步分辨率到更清晰的片状特征。在最慢的下地幔结构下，太平洋中部和南非的速度可以用D”（大约300公里厚）来模拟，剪切速度下降约3%，这与最近的一些断层扫描研究基本一致。在非洲南部地下，一个直径约1200公里的大型结构向上延伸约1500公里，s速度降低约3%。这种异常的边界明显，足以在SKS中产生多路径。南非阵列最近发布的SKS数据显示，SKS旅行时间的跳跃高达8秒，可以等高线，划定了这个巨大结构的清晰度，因为它在印度洋下从西北方向转向东西方向。为了加快开发该结构和太平洋下可能的姊妹结构的3D图像的进展，研究人员计划通过沿选定走廊建模波形数据来集中精力构建整个地幔的2D横截面。将他们的新波形建模工具与pascal阵列和固定站的不断扩展的IRIS网络相结合，将使他们能够解决以下问题：这些巨大结构的侧面有多锋利，它们的3D几何形状是什么；屋顶结构有多均匀，瑞利数是否急剧减少，形成快速移动的小羽流，与660过渡区相互作用，这是否可以在670公里三倍的扭曲中看到；太平洋下的精细结构（SV和SH）是什么？它与中地幔结构有什么关系？研究人员的目的是通过宽带数据收集练习来解决这些问题，然后进行详细的建模，包括所有体波相位采样选定的走廊。

HelmbergerEAR-0229885Considerable progress has been made in mapping out lateral variation in the Earth, demonstrating the active dynamic processes going on beneath us. Advances in seismic tomography in terms of travel time and waveform methodology has allowed major structures in the mantle to be determined. Relatively fast velocities ring the Pacific derived from Global long-period studies and further resolution into sharper sheet-like features with shorter wavelength bodywaves and higher-mode efforts. The velocities beneath the slowest lower mantle structures, mid-Pacific and South Africa can be modeled by a D" (roughly 300 km thick) with about 3% drop in shear velocity in basic agreement with some recent tomography studies. Beneath southern Africa, a large structure about 1200 km across extends upward about 1500 kms with about the same S-velocity reduction of 3%. The boundaries of this anomaly appear sharp enough to produce multipathing in SKS. Recently released SKS data from the South African Array reveals jumps in SKS travel time of up to 8 secs, which can be contoured, delimiting the sharpness of this huge structure as it turns from a northwest direction to an east west direction beneath the Indian Ocean. To make accelerated progress in developing 3D images of this structure and a possible sister structure beneath the Pacific, the investigators plan a concentrated effort to construct whole mantle 2D cross sections by modeling waveform data along selected corridors. Using their new waveform modeling tools in combination with the ever-expanding IRIS networks of PASSCAL arrays and fixed stations will allow them to address the following questions: How sharp are the sides of these huge structures and what is their 3D geometry; how uniform is the roof structure and does the Rayleigh number decrease drastically to form fast moving smaller plumes interacting with the 660 transition zone and can this be seen in distortions of the 670 km triplications; what is the fine-scale structure beneath the Pacific (SV and SH) and how is it related to the mid-mantle structure? The investigators purpose to address these issues with a broadband data gathering exercise followed by detailed modeling, including all body wave phases sampling selected corridors.