Constraining the hydration state of the subducting mantle with converted seismic phases

在会聚的板块边界，水被从地球表面移走。它通过俯冲带进入地球内部，在地球系统的不同部分扮演着许多重要的角色。虽然沉积物和洋壳中储存的水的数量已经通过离岸钻探实验得到了验证，但人们对岩石圈地幔内部的俯冲程度知之甚少。由于测量值很少，问题就产生了：俯冲地幔中储存了多少水？不同俯冲带之间的量有何不同？控制地幔水化的因素是什么？对俯冲板块上方记录的地震记录的分析表明，入射波场发生了从P到S的转换，这表明物质对比位于大洋地幔被认为是水合的大致相同深度。这种转换的特性暗示了该层的各向异性特征。它们表明，各向异性是从海底扩张过程中岩石圈的形成继承而来的，而在俯冲之前的弯曲断裂过程中，另一部分可能是地幔的水化作用。该转换信号可用于估计地震台下方大洋地幔岩石圈的含水率。建议分析陆地地震仪沿所有会聚的板块边界记录的所谓各向异性地幔盖(AML)相对于其厚度和弹性张量的转换。我计划开发一种算法来搜索岩性，因此也就是水含量，这与所发现的AML属性最匹配。随后将该工作流程应用于全球台站组的结果是每个地震台周边的俯冲地幔的含水率。这种对俯冲地幔水的全球汇编可以用来检验有关供水在各种地球过程中所起作用的假设。可以识别控制地幔水化的因素，并以更高的精度估计全球俯冲水收支和速率。

At convergent plate boundaries water is removed from the Earth's surface. It enters the interior of the planet through subduction zones, where it plays a number of important roles in different parts of the Earth System. While the amount of water stored in sediments and the oceanic crust has been validated through off-shore drilling experiments, little is known about how much is subducting inside the lithospheric mantle. As measurements are scarce the questions arise: How much water is stored in the subducting mantle? How does the amount vary between subduction zones? What are the factors that control mantle hydration?The analysis of seismograms that were recorded above subducting plates shows a P-to-S conversion of the incoming wave field that is indicative of a material contrast located approximately at the same depth to which the oceanic mantle is thought to be hydrated. The properties of this conversion hint at the anisotropic character of that layer. They show that anisotropy is to one part inherited from formation of the lithosphere during sea-floor spreading, and to another part likely goes back to hydration of the mantle during bend-faulting prior to subduction. The conversion signal can be used to estimate the water content of the oceanic mantle lithosphere beneath a seismic station.I propose to analyze the conversion of the so-called anisotropic mantle lid (AML) recorded at land seismometers along all convergent plate boundaries with respect to its the thickness and elastic tensor. I plan do develop an algorithm for searching the lithology, and hence water content, that best matches the so found AML properties. The result of the subsequent application of this workflow to a global station set is the water content of the subducting mantle in the perimeter of each seismic station. This global compilation of subducting mantle water can be used to test hypotheses about the role that water supply plays in a variety of Earth processes. Factors that control mantle hydration can be identified, and the global subducted water budget and rate can be estimated with higher accuracy.