CSEDI: Fine Structure of the Lower Mantle

CSEDI：下地幔精细结构

• 批准号: 0456433
• 负责人: Donald Helmberger
• 金额: $ 22.82万
• 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: 2005
• 资助国家: 美国
• 起止时间: 2005-08-15 至 2008-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0456433&HistoricalAwards=false
• 关键词: CSEDI; Fine; Structure; Lower; Mantle

Intellectual MeritSeismologists have known for many years that the lowermost mantle is complex.Attempts at modeling seismic waveforms sampling this region produced ultra-low velocity zones, sharp horizontal discontinuities, strong zones of anisotropy (SHSV), and in some cases near vertical walls. It now appears that this myriad of fine structure is beginning to be understood in terms of mineral physics with dense melts from hot perovskite and a new post-perovskite structure. These new discoveries can explain many of the above features. In particular, the investigators earlier dynamic 2D model of slabs folding at the CMB generates a strong positive velocity gradient, which in turn produces synthetic seismograms containing a small triplication, if a 1% velocity jump is allowed. Assuming that this jump results from a phase-change with a positive Clapeyron slope, and transforming tomographic images through such a hybrid global model, generates some of the geographic behavior of the observed S-wave triplication: where the post-perovskite layer is thickest beneath fast regions and disappears beneath slow regions. The team's latest 3D dynamic models explain the locations of the fastest regions based on the history of plate subduction. Results from 3D dynamics are significantly different from those in 2D, and may help us explain more of the variability in seismic waveform data sampling the lower mantle when seismic and dynamic models are merged. In order to make accelerated progress toward understanding the lower mantle and D" propose research to resolve the 3D nature of these structures. They will address the following questions:o How compatible are 3D dynamic predictions of slab histories with lower mantlestructure? o Can we separate velocity gradient effects caused by subduction from the phase-boundary effects and update a global map?o How different is the mid-Pacific lower mantle structure compared to the Africanstructure and what does this imply in terms of the stability of upwelling?o What dynamic models of thermo-chemical boundary layers are consistent with the proposed post-perovskite structure and seismic data?Broader ImpactAnswers to the above questions will be of great use to the entire Earth Science community, especially mineral physicists who need fundamental seismic information about the global properties of the newly discovered phase boundary. Making the direct connection between the detailed fast structures in the lower mantle with respect to the history of subduction will answer a key question in plate tectonic dynamics. These multi-disciplinary efforts should help the involved students become leaders in future CSEDI developments.

多年来，地震学家们已经知道最低地幔是复杂的。试图模拟该地区采样的地震波形产生了超低速带、尖锐的水平不连续性、强各向异性带（SHSV），在某些情况下接近垂直壁。 现在看来，这种无数的精细结构开始在矿物物理学方面得到理解，其中包括来自热钙钛矿的致密熔体和新的后钙钛矿结构。 这些新发现可以解释上述许多特征。 特别是，研究人员早期的动态2D模型的板折叠在CMB产生一个强大的正速度梯度，这反过来又产生合成地震记录包含一个小的三倍，如果允许1%的速度跳变。假设这种跳跃是由具有正克拉珀龙斜率的相变引起的，并且通过这种混合全局模型转换断层图像，产生了所观察到的S波三重化的一些地理行为：其中后钙钛矿层在快速区域下方最厚，在慢速区域下方消失。 该团队最新的3D动态模型解释了基于板块俯冲历史的最快区域的位置。 从三维动力学的结果是显着不同的，在2D，并可能帮助我们解释更多的变化，在地震和动力学模型合并时，在地震波形数据采样下地幔。 为了加速对下地幔的理解，D”提出了解决这些结构的3D性质的研究。 他们将解决以下问题：如何兼容的三维动态预测板的历史与下mantlestructure？我们能否将俯冲引起的速度梯度效应与相边界效应分开，并更新全球地图？中太平洋下地幔结构与非洲结构相比有何不同？这在上升流的稳定性方面意味着什么？o哪些热化学边界层的动态模型与提出的后钙钛矿结构和地震数据一致？更广泛的影响上述问题的答案将是非常有用的整个地球科学界，特别是矿物物理学家谁需要有关新发现的相边界的全球性质的基本地震信息。 将下地幔中详细的快速构造与俯冲历史直接联系起来，将回答板块构造动力学中的一个关键问题。这些多学科的努力应该帮助参与的学生成为未来CSEDI发展的领导者。