CSEDI Collaborative Proposal: a multi-disciplinary investigation of slab deformation and resulting seismic anisotropy from the transition zone to the base of the mantle

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Over geological time scales, rocks in Earth’s deep interior flow like fluids. The deformation and advection of rocks within the Earth are concrete expressions of mantle thermal convection. Mantle convection drives plate tectonics near Earth’s surface and controls the long-term evolution of the planet. For this project, a team of scientists from different research fields - including seismology, mineral physics, and geodynamics - collaborate to better understand the nature of mantle convection. When earthquakes happen, the energy propagates through Earth’s interior in the form of seismic waves. The speed of seismic waves traveling through rocks in one direction is often different from that in another direction. This phenomenon is called seismic anisotropy. Seismic anisotropy of rocks is controlled by their mineral structure and the nature of the surrounding mantle flows. Here, the researchers use super-computers to simulate mantle flow fields. They perform mineral physics experiments to study the deformation mechanisms of mantle minerals. They analyze seismic waves to understand mantle seismic anisotropy. The predicted mantle flow fields are combined with new understanding of mineral deformation to predict seismic anisotropy, which is then compared with observations. The aim is to provide new insight into the structure and dynamics of Earth’s deep interior. This project fosters inter-disciplinary collaboration and provides support to 3 graduate students, 1 postdoctoral associate and 1 early-career scientist. Teaching materials will be produced, which will be used in undergraduate and graduate classes and in educational outreach to the public through outreach events and via the internet. Analytical and modeling software will become available to general users.Over the past few decades, seismic anisotropy has been observed mainly in Earth’s uppermost and lowermost mantle. Yet, accumulating evidence suggests the presence of significant seismic anisotropy in the transition zone and the uppermost lower mantle. The nature of uppermost mantle seismic anisotropy is relatively well established, and some consensus exists to first order on the large-scale distribution of anisotropy in D". There is, however, little consensus on the character and strength of seismic anisotropy in the mantle transition zone and the uppermost lower mantle. It remains unclear at these depths how seismic anisotropy is related to mantle flow and the deformation mechanisms of mantle minerals. Interpreting seismic observations in the context of mantle dynamics requires input from mineral physicists and geodynamicists; they can relate the seismic velocities and anisotropy to temperature, composition, and deformation of the corresponding materials. Here an interdisciplinary team of seismologists, geodynamicists, and mineral physicists aim to further advance the understanding of the seismic and viscosity structures, and the nature of mantle flow in two regions: 1) the D" layer, in continuation of their previous works; (2) the extended transition zone located at depths ranging from ~400 to 1000 km within the Earth.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.