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

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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.