High-Frequency Seismic Scattering at the Core Mantle Boundary: Insights from Radiative Transfer Equation and Wave Equation Modelling

High-frequency seismic scattered waves provide unique sensitivity to small-scale heterogeneity in the lowermost mantle and at the core mantle boundary (CMB), but their interpretation is challenged by wavefront healing and the huge cost of full-waveform simulations at frequencies above about 1 Hz. We evaluate the precision of radiative transfer equation (RTE) modelling compared with wave equation (WE) modelling to establish a basis for future coupled RTE-WE approaches to high-frequency seismic scattering at the CMB.

We have used the RTE based on the Monte Carlo method to efficiently simulate the global transport of seismic energy with a 1D spherical symmetrical model and reproduced scattered waves, such as PKP precursors and Pdiff coda. Now, WE simulations are employed in localised CMB domains to resolve deterministic wave structure interactions, including scattering, interference, and diffraction. Forward models are constructed from the CMB and D” layer, including layered structures, CMB topography, ultra-low velocity zones, and distributed volumetric heterogeneity. We analyse full waveform simulations in terms of their associated energy distributions and envelopes, and explore how these waveform-derived quantities can be related to seismic intensities modelled by RTE under different structural cases. This framework provides a way toward coupling RTE simulations with WE modelling in further studies, enabling detailed investigation of CMB structure using localised wave equation modelling while substantially reducing the computational cost of global high-frequency simulations.