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At the core-mantle boundary, most observed ultralow velocity zones (ULVZs) cluster along the edges of the large low shear velocity provinces (LLSVPs) and provide key information on the composition, dynamics, and evolution of the lower mantle. However, their detailed structure near slab-like structures beneath the mid-Pacific remains particularly challenging because of the lack of station coverage. While most studies of ULVZs concentrate on SKS-complexity, here we report on the multipathing of ScS, which expands the sampling for ULVZs. We find the strongest multipathing along a ULVZ patch located just south of Hawaii and the far northeastern edge of the LLSVP, in a zone similar to 200 km in width and extending 600 km southward. The anomalous ScS travel times and distorted S-diff waveforms further reveal patches interrupted by observed enhanced D '' indicative of slab-debris influence on the complexity of the northeastern boundary of the mid-Pacific LLSVP.

Plain Language Summary Mapping the detailed boundaries of the large low shear velocity provinces at the core-mantle boundary is one of the keys to understanding the dynamics of the lower mantle. However, imaging the lower mantle beneath mid-Pacific is difficult because of the limited seismic ray coverage and seismic phases used. In this study, we identify a new seismic signal, multipathing of ScS, which can be modeled with an ultralow velocity zone sitting at the far edge of the mid-Pacific large low shear velocity province. The locations of the ultralow velocity zone and the nearby slab demonstrate that the complexities of the northeastern boundary of the mid-Pacific LLSVP are strongly affected by the slab reaching to the core-mantle boundary.