CSEDI: A Joint Seismological and Mineral Physics Approach to Unravel the Origin of Lower Mantle Heterogeneity

CSEDI：揭示下地幔非均质性起源的地震学和矿物物理联合方法

• 批准号: 0652985
• 负责人: Quentin Williams
• 金额: $ 21.11万
• 依托单位: University of California-Santa Cruz
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-04-01 至 2010-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0652985&HistoricalAwards=false
• 关键词: CSEDI; Joint; Seismological; Mineral; Physics

Seismic tomography provides images of the fast and slow regions within the Earth's lower mantle using the travel times of a variety of body waves produced by earthquakes and recorded at seismometers around the globe. The investigators are examining the seismic and mineralogical behavior of the tomographically fastest regions of the lower mantle. The goal is to discover whether or not fast anomalies are uniformly associated with subducted material, and to resolve the likely effects of temperature and composition in generating these anomalies. Recent seismic tomographic models have excellent resolution in the mid and lower mantle and reveal a change in character with depth of fast anomalies. In the mid mantle, fast anomalies resemble linear features that can be associated with paleo-subduction zones. In the lower mantle, the fast anomalies take on a circum-Pacific pattern that essentially wraps around the large slow velocity provinces under the central Pacific and Africa that rise from the core-mantle boundary. In the canonical view of whole-mantle convection, seismically fast subducting oceanic lithosphere descends to the core-mantle boundary, where it drives the flow of the passive, seismically slow material. While much attention has been paid to detailed investigations of these slow features, the seismic characteristics of the fast features are poorly documented. We plan to use the most current catalog of long-period travel times of lower mantle S, P, Sdiff, Pdiff, ScS, SKS, and PKP phases to better-define the shear, compressional, and bulk sound speed of these anomalies in the lower mantle. The investigators are developing a formulation for the relative variations of these seismic waves that is interpretable from a mineral physics framework, and which is suitable for investigating 3D structure. Presently, the seismic behavior of basalt is not well understood in the lower mantle, but the investigators' preliminary calculations indicate that it is a likely candidate for producing fast seismic velocities. The investigators are using an iterative approach to discern whether the fast anomalies can be explained simply as thermal anomalies, or it they require a contribution from a fast component such as oceanic basalt, and if so, in what quantity. The investigators are also probing the anomalies with short-period seismic data from regional arrays that sample the fast features. If reflectors or velocity gradients are present, they will provide additional constraints on the thermo-chemical state of the material. Near the core-mantle boundary, the investigators anticipate that some of the fast anomalies may not be generated by temperature and/or chemical anomalies, and may require incorporation of the seismic characteristics of the post-perovskite phase transition into their thermo-chemical models. This project is funding the postdoctoral work of Dr. C. Reif who has made major contributions to Earth science outreach in elementary schools and the general community, and who is continuing her work to meet the needs of Earth science K-12 educators in the Santa Cruz area.

地震层析成像利用地震产生的各种体波的传播时间，提供地球下地幔内快速和慢速区域的图像，并记录在地球仪周围的地震仪上。 研究人员正在检查下地幔断层扫描最快区域的地震和矿物学行为。 目标是发现快速异常是否与俯冲物质一致相关，并解决温度和成分在产生这些异常时可能产生的影响。 最近的地震层析成像模型在中下地幔具有很好的分辨率，并揭示了快速异常的特征随深度的变化。 在中地幔，快速异常类似于线性特征，可以与古俯冲带。 在下地幔中，快速异常呈现环太平洋模式，基本上包裹着从核幔边界升起的中太平洋和非洲下的大型低速区。 在全地幔对流的典型观点中，地震快速俯冲的海洋岩石圈下降到核幔边界，在那里它驱动被动的、地震缓慢的物质流动。 虽然对这些慢特征的详细调查已经引起了很大的注意，但对快特征的地震特征的记录却很少。 我们计划使用最新的下地幔S，P，Sdiff，Pdiff，ScS，SKS和PKP相位的长周期旅行时间目录，以更好地定义下地幔中这些异常的剪切，压缩和整体声速。 调查人员正在开发一种公式，用于这些地震波的相对变化，可以从矿物物理学框架中解释，并且适合于调查3D结构。 目前，玄武岩在下地幔中的地震行为还没有得到很好的理解，但研究人员的初步计算表明，它是产生快速地震速度的可能候选者。 研究人员正在使用一种迭代方法来辨别快速异常是否可以简单地解释为热异常，或者它们是否需要来自海洋玄武岩等快速成分的贡献，如果是的话，数量是多少。 调查人员还利用区域阵列的短周期地震数据对这些异常进行了探测，这些数据对快速特征进行了采样。 如果存在反射器或速度梯度，它们将对材料的热化学状态提供额外的约束。 在核幔边界附近，研究人员预计，一些快速异常可能不是由温度和/或化学异常产生的，可能需要将后钙钛矿相变的地震特征纳入其热化学模型。 该项目资助了C博士的博士后工作。赖夫谁作出了重大贡献，地球科学在小学和一般社区的推广，谁是继续她的工作，以满足地球科学K-12教育工作者在圣克鲁斯地区的需求。