What are the seismic expressions of deep thermal and thermochemical plumes?

夏威夷和冰岛是与来自地幔深处的动力上涌(即羽流)有关的火山岛的典型例子。在对地球对流的实验室模拟中，羽流自然而丰富地形成。然而，地球科学家之间并没有达成共识，地球上是否存在上升的羽流。地震学家的重任是在地震数据中寻找羽流的表现形式。这项提议的目的是确定物理上看似合理的热和热化学羽流如何干扰地震波，以及如何在地震数据中发现这些扰动。该项目将支持一名博士生。这项研究扩展了正在进行的国际合作，为密歇根的博士生和两名直接参与该项目的欧洲学生提供了重要的国际经验。这项建议利用了美国国家科学基金会在观测地球物理(包括地球望远镜和专用地震阵列)方面的大量投资，使用现有数据，并提供了一种新的跨学科调查，以了解观测地球物理对地幔热柱的分辨能力。通过结合多学科的专业知识，这项建议中的工作将开发对热柱形成和热柱形态的高分辨率模拟，并将量化地震数据中预期的热柱特征。这项研究包括热和热化学羽流上升的计算机模拟，羽流内地震波速变化的矿物物理计算，以及羽流对地震波场扭曲的三维模拟。对模拟波形的波形和旅行时层析成像以及接收器函数分析将展示羽流是如何层析成像的，以及它们是否在过渡区产生明显的相界偏转。

Hawaii and Iceland are classic examples of volcanic islands associated with dynamical upwellings (i.e., plumes) from the deep mantle. Plumes form naturally and abundantly in laboratory simulations of Earth convection. Yet, there is no consensus among Earth scientists whether rising plumes exist in the Earth. The burden is on seismologists to find expressions of plumes in seismic data. This proposal is aimed at identifying how physically plausible thermal and thermochemical plumes may perturb seismic waves and how these perturbations can be found in seismic data. The project will support one PhD student. The research expands an ongoing international collaboration that provides important international experience to the PhD student at Michigan and the two students in Europe who are directly involved in the project.This proposal leverages significant investments made by the NSF in observational geophysics (including EarthScope and dedicated seismic arrays) by using the available data and providing a new, interdisciplinary investigation into the resolvability of mantle plumes by observational geophysics.By combining multidisciplinary expertise, the work in this proposal will develop high-resolution simulations of plume formation and plume morphology and it will quantify the expected plume signatures in seismic data. The research involves computer simulations of thermal and thermochemical plume ascent, mineral physics calculations of the seismic wave speed variations within plumes, and 3D simulation of the distortion of the seismic wave field by plumes. Waveform and traveltime tomography and receiver function analysis of simulated waveforms will demonstrate how plumes are imaged tomographically and whether they produce observable deflections of phase boundaries in the transition zone.