Mapping Chemical Plumes from Bottom to Top

从下到上绘制化学羽流图

• 批准号: 0229885
• 负责人: Donald Helmberger
• 金额: $ 27.52万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-11-15 至 2005-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0229885&HistoricalAwards=false
• 关键词: Mapping; Chemical; Plumes; Bottom; Top

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.

在绘制地球横向变化图方面已经取得了相当大的进展，显示了我们下面正在发生的活跃的动态过程。 地震层析成像在走时和波形方法方面的进展使人们能够确定地幔中的主要结构。 相对较快的速度环太平洋来自全球长周期的研究，并进一步分辨率为更清晰的片状特征与较短波长的体波和更高的模式的努力。 最慢的下地幔结构、中太平洋和南非的速度可以用D”（大约300 km厚）来模拟，剪切速度下降约3%，与最近的一些层析成像研究基本一致。 在南部非洲之下，一个大约1200公里宽的大结构向上延伸了大约1500公里，S速度降低了3%。 这种异常的边界看起来足够尖锐，足以在SKS中产生多路径。 最近发布的南非阵列SKS数据显示，SKS旅行时间的跳跃长达8秒，可以进行轮廓，界定这个巨大结构的锐度，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方可能的姐妹结构的3D图像的进展，研究人员计划集中精力，通过对沿着选定走廊的波形数据进行建模，构建整个地幔的2D横截面。 使用他们新的波形建模工具，结合不断扩展的PASSCAL阵列和固定站的IRIS网络，将使他们能够解决以下问题：这些巨大结构的侧面有多尖锐，它们的3D几何形状是什么;屋顶结构的均匀性如何？瑞利数是否急剧减少，从而形成快速移动的较小羽流，与660度的过渡区相互作用？在670公里的三重扭曲中看到的是什么？太平洋（SV和SH）下的精细尺度结构是什么？它与中地幔结构有什么关系？研究人员的目的是解决这些问题的宽带数据收集练习，然后详细建模，包括所有体波相位采样选定的走廊。