Work

Uniform automated analysis of S diff splitting due to lowermost mantle anisotropy: caveats and curated global data set

Year: 2026

Type: article

Abstract: SUMMARY Seismic anisotropy, the dependence of seismic wave speeds on the direction of propagation and/or polarization, places crucial constraints on deformation and convective flow in the lowermost mantle (the D$^{\prime \prime }$ layer). Shear waves that diffract along the core–mantle boundary (CMB) are ideally suited for probing this region due to their long horizontal ray paths in the lowermost mantle. However, the inference of D$^{\prime \prime }$ anisotropy presents multiple methodological challenges, including the need for accurate upper mantle corrections and the potential for apparent splitting produced by isotropic structures. In this study, we leverage global wavefield simulations to develop an automated measurement procedure that excludes Sdiff waves that are strongly SVdiff-polarized, which can lead to apparent splitting even in the absence of seismic anisotropy. We apply this workflow to a global data set of ${\sim }20$ million three-component seismograms. By adhering to strict quality control criteria, we generate a highly regionally consistent data set of high-confidence measurements. Overall, we obtain ${\sim }4300$ Sdiff splitting measurements that constrain the presence or absence of D$^{\prime \prime }$ anisotropy. We project these measurements onto the D$^{\prime \prime }$ layer and report Sdiff splitting across 237 global geographic bins (approximately 28 per cent of the D$^{\prime \prime }$ layer by surface area) with sufficient data coverage. Of these, 55 bins exhibit clear splitting, many of which are located beneath the northern Pacific. Furthermore, we characterize the directional dependence of splitting using binning algorithm by local propagation azimuth for regions with multidirectional coverage. We make this curated data set of geographically and directionally binned Sdiff splitting measurements, along with all codes necessary to reproduce it, publicly available.

Source: Geophysical Journal International

DOI: 10.1093/gji/ggag393

Authors: Alex Sun, Jonathan Wolf, Barbara A Romanowicz, Ed Garnero, John D West

Institutions: University of California, Berkeley, Planetary Science Institute, University of California, Santa Cruz, Arizona State University

Language: English

Topic: High-pressure geophysics and materials

Subfield: Geophysics

Field: Earth and Planetary Sciences

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $3,416

Funder: National Science Foundation