ABSTRACT

Seismic waves generated by earthquakes travel all around the globe and carry information from the deep interior of our planet. Seismologists analyze these seismic waves and make measurements compared to simulated data to illuminate the complexities of the Earth's interior. The measurements are then used in a technique called seismic tomography, similar to medical tomography, to obtain 3D CAT-scan images of the crust and mantle in terms of seismic parameters. Advances in supercomputers and numerical methods, together with the increase in the quality and amount of seismic data in recent years, have provided new opportunities to improve the resolution of tomographic images based on 3 dimensional numerical wave simulations. High-resolution present-day snapshots of Earth's interior are essential for understanding the past and present dynamics of the mantle, which shape the surface of our planet through tectonic processes such as earthquakes and volcanic activities. Higher-resolution models are also crucial for better understanding the source of earthquakes, accurately locating them, and are required from an engineering point of view to assess seismic hazard and to detect nuclear explosions. To facilitate effective exploration of Earth's mantle for research and educational activities, constructed models together with data from other disciplines will be used to design an interactive, collaborative Earth model, SPAC-MAN (Slabs, Plumes And Convection in MANtle), for visualization in virtual and augmented reality environments and planetariums. The collaboration with the Denver Museum of Nature & History will reach a range of age groups from children to adults, educating them on the interior of our planet and its dynamics while promoting STEM fields.

Seismic imaging of the mantle's multi-scale structure provides fundamental constraints to frame and understand present-day mantle dynamics. Attenuation, a measure of the energy loss of seismic waves, is a key parameter to detect partial melt, thermal variations, and water content in the mantle. Since attenuation may also significantly affect arrival times of seismic phases, wavespeed and attenuation models should be constructed together simultaneously. The goal of this CAREER proposal is to investigate the multi-scale structure of the mantle based on 3D seismic wave simulations and the simultaneous construction of seismic wavespeed and attenuation models. Emerging data sets from oceans will also be explored to assimilate them in seismic tomography to specifically improve the resolution underneath oceans. Seismic tomography is at a stage where further refinements in the resolution require the use of full physics of wave propagation. Adjoint tomography, a full-waveform inversion technique, efficiently takes advantage of 3D wave simulations leading to pure data-driven seismic models of the Earth's interior avoiding commonly used approximations and corrections in classical seismic tomography. The goal of this CAREER proposal is to provide new constraints on the multi-scale (an)elastic structure of Earth's mantle based on 3D wave simulations and full-waveform inversion. To this end, (1) an anelastic global mantle model will be constructed by simultaneously inverting for anelastic and elastic parameters based on global full-waveform inversion, which will avoid bias that may come from ignoring scattering/defocusing effects. (2) multi-scale heterogeneity throughout the mantle will be investigated through their forward modeling, (3) a framework will be constructed to assimilate emerging data sets from oceans into global adjoint inversions to improve global data coverage and the resolution of oceanic plumes. The project outcomes will provide critical parameters to mineral physicists and geodynamicists to have better insight into the composition and thermal evolution of our planet, facilitating interdisciplinary research.

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.

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