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

在汇聚的板块边界，水从地球表面消失。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。虽然储存在沉积物和海洋地壳中的水量已经通过海上钻探实验得到了验证，但人们对岩石圈地幔内部俯冲的水量知之甚少。由于缺乏测量数据，问题出现了：俯冲地幔中储存了多少水？不同的俯冲带之间的含量有什么不同？控制地幔水合作用的因素是什么？对记录在俯冲板块上方的地震图的分析显示，入射波场的p - s转换表明，物质对比大约位于海洋地幔被认为是水合的同一深度。这种转换的性质暗示了该层的各向异性特征。结果表明，各向异性一方面继承自海底扩张过程中岩石圈的形成，另一方面可能源于俯冲前弯曲断裂过程中地幔的水化作用。转换信号可用于估算地震台站下的海洋地幔岩石圈含水量。我建议分析陆地地震仪沿着所有收敛板块边界记录的所谓各向异性地幔盖（AML）的厚度和弹性张量的转换。我计划开发一种算法来搜索岩性和含水量，从而与已发现的AML属性最匹配。随后将此工作流程应用到全球台站集的结果是每个地震台站周围俯冲地幔的含水量。这种俯冲地幔水的全球汇编可以用来检验关于水供应在各种地球过程中所起作用的假设。通过对地幔水化控制因素的识别，可以较准确地估算出全球俯冲水量平衡和速率。

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.