Seismic low-velocity equatorial torus in the Earth’s outer core: Evidence from the late–coda correlation wavefield

Abstract

Thermochemical inhomogeneities in the Earth’s outer core that enhance our understanding of the geodynamo have been elusive. Seismic constraints on such inhomogeneities would provide clues on the amount and distribution of light elements in the core apart from iron and nickel. Here, we present evidence for a low-velocity volume within the outer core via the global coda correlation wavefield. Several key correlogram features with a unique sensitivity to the liquid core show variations with wave paths remarkably slower in the equatorial than polar planes. We constrain a torus structure at low latitudes with ~2% lower velocity than the surrounding liquid outer core via waveform modeling. We propose a thermochemical origin for such a low-velocity torus, providing important constraints on the dynamical processes of the Earth’s outer core.