Finite-frequency Imaging of the Mantle Transition Zone Discontinuities

由于压力的增加，地球次表层的矿物在大约410公里和660公里深处的地幔过渡带经历了主要的相变。地幔过渡带的过程对浅部上地幔与深部下地幔之间的物质交换具有重要的制约作用。这些都是导致板块构造、地震和火山爆发的动态过程。这项研究利用一种新的地震成像理论和世界各地地震台站收集的数据来绘制地幔过渡带的结构图。这项研究旨在促进对地幔动力学的了解，重点是全球大洋区的主要俯冲带(块状大洋板块俯冲到地幔深处)以及火山热点。地幔过渡带的高分辨率图像将提供给更广泛的地球科学界，用于未来的多学科研究。基于这项研究的实践课程项目和实验室将在本科教学中开发和实施，并将对研究生进行支持和培训。板块拉动通常被认为是驱动全球构造板块运动的主导力量。这种对流模式在上地幔受到很好的约束，但中地幔的对流模式更具投机性。这项研究将建立一个SS前兆有限频率旅行时间测量的全球数据集，以基于行波模式耦合框架下计算的天生灵敏度来成像410公里和660公里不连续面的全球结构。GSN和US阵列站的有限频率接收器功能测量将用作补充数据集，以提高大陆以下的区域分辨率。新的高分辨率MTZ不连续模型将与已发表的地震波速和各向异性模型一起分析，以促进对地幔过渡区地球过程的基本了解，重点是俯冲带中停滞板块的结构和动力学以及海洋热点下的热和成分变化。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Due to increased pressure, minerals in the Earth’s subsurface undergo major phase transitions in the mantle transition zone at depths of about 410 km and 660 km. Processes in the Earth's mantle transition zone provide important constraints on the mass exchange between the shallower upper mantle and the deeper lower mantle. Those are dynamic processes that are responsible for plate tectonics, earthquakes and volcanoes. This research takes advantage of a new seismic imaging theory and data collected by seismic stations around the world to map the structure of the mantle transition zone. This research aims to advance understanding of mantle dynamics with focuses on major subduction zones (where massive oceanic plates subduct into the deep mantle) as well as volcanic hotspots in global oceanic regions. High-resolution images of the mantle transition zone will be made available to the broader Geosciences community for future multidisciplinary studies. Hands-on course projects and labs based on this research will be developed and implemented in undergraduate teaching, and a graduate student will be supported and trained. Slab pull is generally considered as the dominant force that drives the global movement of tectonic plates. This convection mode is well constrained in the upper mantle but the convection pattern in the mid mantle is more speculative. This research will build a global dataset of finite-frequency travel time measurements of SS precursors to image the global structure of the 410-km and 660-km discontinuities based on Born sensitivities calculated in the framework of traveling-wave mode coupling. Finite-frequency receiver function measurements at GSN and USArray stations will be used as complementary datasets to improve regional resolution beneath continents. The new high-resolution MTZ discontinuity models will be analyzed together with published seismic wave speed and anisotropy models to advance fundamental understanding of Earth processes in the mantle transition zone, with focus on the structure and dynamics of stagnant slabs in subduction zones as well as thermal and compositional variations beneath oceanic hotspots.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.