Do thermochemical convection models explain wave propagation and scattering?

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The theory of Plate Tectonics is a theory of Earth dynamics. The movements of tectonic plates cause earthquake faulting and volcanic eruptions, they result in the uplift of Earth's mountain ranges, and they explain the complexity of geologic formations around the world. However, it remain unclear how plate tectonics is tied to large-scale rock flow in Earth's interior. Near tectonic collision zones, the oceanic lithosphere descends deep into Earth's interior, in some places to the bottom of the mantle at a depth of about 1800 miles. The compositionally distinct crust is carried along with the oceanic plate. It will separate from the plate and circulate freely within the mantle. Since this process has been ongoing for billions of years, we expect that 10 to 100 mile size chunks of the crust have been dispersed throughout the mantle. Mapping the variable concentration of these fragments of the crust in the mantle will help us understand how Earth's interior is flowing. The project will support one PhD student and several undergraduate students via the Undergraduate Research Opportunities Program at U Michigan. The research expands an ongoing international collaboration that provides important international experience to the PhD student at Michigan and students in Japan, China, and the United Kingdom who are directly involved in the project.The mixing of ancient crust in the mantle depends on the density of the crust with respect to the ambient mantle and the vigor of flow in the mantle. The team's research is aimed at constraining these parameters by studying how earthquake generated seismic waves are scattered by crustal fragments in the deep mantle. They will study seismic wave scattering from an experimental and theoretical point of view. An international team of investigators will work with rock physicists to constrain the density and elastic properties of crustal fragments at the high-temperature and high-pressure conditions deep in Earth's mantle. They will map seismic wave scattering using roughly 150,000 seismograms from the Global Seismic Network and from the USArray, a network of seismographs in the United States that has been operating during the past decade. The investigators will simulate seismic wave scattering using computer simulations of mantle mixing and by computing seismic wave scattering on high-performance computers. Using this joint approach, they hope to constrain the vigor of mantle flow and to understand whether the settling of dense crustal fragments at the base of the mantle explains broad regions of compositional heterogeneity in Earth's deep interior. The research will add to understanding of our planet's evolution and how plate tectonics works.