Collaborative Research: Investigating formation of stagnant slabs and implications for subduction dynamics

自板块构造理论建立以来，已经过去了几十年。科学家们仍在争论板块如何循环进入地球内部，随着时间的推移它们是如何下降的。在生成地球的“地震断层图像”(类似于医学CT扫描)方面的进步提供了这些沉没的板块(或称“板块”)的越来越详细的图像，其中许多板块被困在地球表面下约300至600英里处。这些图像代表了对流地幔的现代快照，可以通过俯冲过程的数值模拟来研究其随时间的演变。这一合作提议结合了数据驱动建模和地震层析成像方面的最新发展。刘、特罗姆和他们的研究生将探索俯冲板块被困在地幔中段的不同方式，重点放在两个相互矛盾的假设上：板块被粘在地表的板块上的一端拉动，或(2)它随着周围地幔的水平流动而被拖曳。这项研究将提高我们对地幔如何流动以及几千万年来它是如何流动(以及地球板块如何移动)的理解。用于模拟板块和地幔成像的复杂软件将得到显著改进，并通过公共网站与其他科学家免费分享。500-1000公里地幔深度范围内的广泛快速地震异常被称为停滞板块，它们的成因对大陆构造和地幔动力学具有意义。一种常用的机制是战壕撤退，但观察到的撤退数量并不总是与模拟相符。另一个经常被提出的假设是，楼板垂直下沉，尽管这可能违反地质观测。这些问题的一个潜在解决方案是考虑中地幔深处的侧向地幔流动，其对板块停滞的影响仍未得到很好的研究。另一个复杂的问题是，目前停滞不前的平板的断层图像不一致。PI团队将通过顺序数据同化(SDA)设计3D球面地球模型，并将结果与使用全波形反演(FWI)和震源编码的改进层析图像进行比较，从而合作评估海沟后退和横向地幔流动对板块停滞的动态影响。SDA建模方法适合于测试板坯停滞的关键控制参数，同时考虑了许多其他自然复杂性。改进的FWI方法显著提高了停滞板块所在的中上地幔深度的地震分辨率。通过一套SDA模型，测试在区域和全球尺度模拟中实施的不同地理位置的海沟运动历史的可用范围，研究小组将量化海沟后退和横向地幔流动对观测到的停滞板块形成的各自贡献。最终，这项工作将产生对俯冲动力学和相关构造记录的新见解。这一奖项反映了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。

Many decades have passed since the establishment of the theory of plate tectonics. Scientists still debate how tectonic plates recycling into Earth’s interior evolve over time as they descend. Advances in generating 'seismic tomographic images' of the Earth (analogous to medical CT scans) provide increasingly detailed images of these foundered plates (or 'slabs'), many of which are trapped about 300 to 600 miles below the Earth's surface. These images represent a present-day snapshot of the convecting mantle, and its evolution over time may be investigated through numerical modeling of the subduction process. This collaborative proposal combines recent developments in data-driven modeling and seismic tomography. Liu, Tromp, and their graduate students will explore different ways that subducted slabs get trapped in the mid mantle, with a focus on two competing hypotheses: that the slab is being pulled by one end which is stuck to a plate at the surface, or (2) that it is dragged along with horizontal flow of the surrounding mantle. This research will improve our understanding of how the Earth's mantle flows, and how it has flowed (and how the Earth's plates have moved) over tens of millions of years. Sophisticated software for modeling the slabs and imaging the mantle will be significantly improved and freely shared with other scientists via public websites.Extensive fast seismic anomalies within the 500-1000 km mantle depth range are called stagnant slabs, and their origin has implications for continental tectonics and mantle dynamics. A commonly invoked mechanism is trench retreat, but the observed amount of retreat does not always match simulations. Another frequently made assumption is that slabs sink vertically, even though this can violate geological observations. A potential solution to these problems is to consider lateral mantle flow at mid-mantle depths, whose effect on slab stagnation remains poorly explored. Another complication is the inconsistency of tomographic images of the present-day configuration of stagnant slabs. The PI teams will collaboratively evaluate dynamic effects of trench retreat and lateral mantle flow on slab stagnation by designing 3D spherical Earth models through sequential data assimilation (SDA) and comparing the results with improved tomographic images using full-waveform inversion (FWI) with source encoding. The SDA modeling approach is appropriate for testing key controlling parameters for slab stagnation while simultaneously considering many other natural complexities. The improved FWI method increases seismic resolution significantly at upper-to-mid mantle depths, where stagnant slabs reside. Through a set of SDA models that test the available range of trench motion histories at different geographic locations implemented in both regional- and global-scale simulations, the teams will quantify the respective contributions of trench retreat and lateral mantle flow on the formation of observed stagnant slabs. Ultimately, this exercise will generate new insight into subduction dynamics and the associated tectonic records.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.