NSFGEO-NERC: Advancing capabilities to model ultra-low velocity zone properties through full waveform Bayesian inversion and geodynamic modeling

Ultra-Low Velocity Zones (ULVZs) are structures with strongly reduced seismic velocities at Earth's core-mantle boundary (CMB) which have been associated with or linked to hot-spot volcanism, Large Igneous Provinces, core-mantle interaction, downwelling subduction and Large-Low Velocity Provinces (LLVPs)

and thus are a critical component of global mantle dynamics. ULVZs are typically studied using waveform analysis of ULVZ-sensitive seismic probes (e.g., SPdKS, ScP, ScS), but previous studies suffer from large uncertainties in ULVZ parameters due to modeling trade-offs and lack a geophysical inference of ULVZs

through rigorous parameter estimation. We seek to develop a transformative waveform inversion approach and apply it to characterize ULVZ properties including their seismic velocities, density, size, and shape. Specifically, we propose to (1) collect a new database of highly ULVZ-sensitive ScP and PcP waveforms utilizing publicly available seismic array

data as well as new data from South Korea, Taiwan, Japan, and the International Monitoring System (IMS) arrays, (2) advance our capabilities for full waveform Bayesian inversion for ULVZ properties in order to quantitatively distinguish regions with and without ULVZ structures (i.e., Bayesian model selection), and

to perform joint inversion of ScP and PcP waveforms, (3) quantify the waveform effects from 2-D/3-D ULVZ structures, (4) search for additional, previously unlooked-for arrivals in the ScP wavefield consistent with 3-D ULVZ structure using array processing approaches, and (5) relate observed ULVZ localities and

properties to lowermost mantle flow and dynamics through 3D geodynamic models.