Mapping Lowermost Mantle Seismic Structures With Core‐Diffracted Waves
Journal
Journal of Geophysical Research: Solid Earth
Journal Volume
131
Journal Issue
6
ISSN
2169-9313
2169-9356
Date Issued
2026-06
Author(s)
Abstract
Pdiff and SHdiff waves, diffracted along the core-mantle boundary (CMB), are highly sensitive to the structures of the lowermost mantle (LMM). Using an automated procedure, we measure the absolute traveltime residuals ((Formula presented.), (Formula presented.)) from cross-correlation (cc) between observations and synthetics for (Formula presented.) 2.02 million Pdiff + P and (Formula presented.) 1.96 million SHdiff + SH waves in multiple period bands. The gridded mean (Formula presented.) and (Formula presented.), (Formula presented.) and (Formula presented.), exhibit a degree two pattern consistent with the Large Low Shear-Velocity Provinces (LLSVPs) observed in global seismic tomography models beneath Africa and the Pacific. Furthermore, the (Formula presented.) are 2–3 times stronger than (Formula presented.), and (Formula presented.) under the African LLSVP are stronger than under the Pacific LLSVP by a factor of 2–3. The distribution of the (Formula presented.) ratio shows a broad, dispersive pattern, with the majority of the population between −2 and +5, in contrast to purely thermal effects, which predicted a (Formula presented.) ratio in the range of 1.7–2.6. Finally, the (Formula presented.) distribution is skewed to low velocity, while the (Formula presented.) distribution is Gaussian. Collectively, these observations point to thermochemical LLSVPs.
Subjects
core-mantle boundary
diffracted waves
lowermost mantle
seismic structures
Publisher
American Geophysical Union (AGU)
Type
journal article